Making PIC Microcontroller Instruments and Controllers

Harnessthe powerof the PIC microcontrollerunit with practical,commonexpert.Througheightreal-world instructionftom an engineering sense projects,clearillustrations,and detailedschematics, MaftingP1C@ Instruments andControllers showsyou,step-by-step, Microcofitroller how to designandbuild versatilePIC-baseddevices.Configureall necessary hardwareand software,readinput voltages,work with control pulses, interfacewith peripherals,and debugyour results.You'll alsogetvaluable anda list of sample coveringtechnicalterms,abbreviations, appendices prograrns available online.

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MAKING PIC@ MICROCONTROLLER I]ISTRUMENTSAND CONTROLLERS

MAKING PIC@ MICROCONTROLLER INSTRUMENTS AND CONTROLLERS HARPRITSINGH SANDHU

NewYork Chicago San Francisco Lisbon London Madrid MexicoCily Milan NewDelhi SanJuan Seoul Singapore Sydney Toronto

Library of CongressCataloging-in-Publication Data Sandhu, Harpdt. jnstruncntsandconrrcllcn/ Haurit SinghSandhu. MakingPIC nricrccontrcllcr hcludcs bibliogtuphicalrciircDccs lnd indcx. (alk.talef) ISAN 978-0-07-160616-5 l. Microcontrollc$.2. Elcctronicappamtusand appliuccs L Tirlc, TJ223.P76537 2009 6 2 1 . 3 9 1 6d c 2 2

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2008049998 McGruwHill booksrre alailable.t specialquantiry discounts to users premiumsand saleslr()nolbns. or lor useio corporatelraininSprcgran$.To conta.ta specialsales pleasevisil lheContaclUs pageal www rnhprcfesioral.con. represenl.tive. Making PlCoMicrocontrollcrInstrumcntsand Controllcrs CopyrigltO 2009by Thc McGL{w-HillConprnics,hc Allr'iglrtsrlscNcd.Pr'i cd in thc UnhcdSt{rtcsof AmcriQ. lxccpt rs pcLDiitcdundcrthc Unilcd Sl ics Copyrigllt Acr ol 1976.io partol this tublicatn!1mdy hc rcpn)duccd or disributcdin any li)an or by rny mems.or storcdin x daLxbNe or relricvrlsystcnr,wilhoutlhe prid wri(ten pcnnission ol lhc ptrhlisher. t 2 t 4 5 6 7 8 9 0

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Intenrdion!'l TypesettinS.nd Contposirion Intemrlion.lTypesertirg.nd Conrposirion CopyEditor MichaelMccee

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Irtbrnltion contaircd h this wofk hls bccn obtaincdby Thc Mccfaw-llill Companics, hrc. ( Mccraw Hill ) tiom sourccsbclicvcd10bc rclilblc. Howcvcr. guarantee nenherMccfuw-Hill nor ns auLhors theaccuracyor conpleteness ol any infonnadonpoblishedberein.and nenherMccraw Hill nor its atrdo^ shall be respo.sible for anyerors, onrlssions, or dimaeesarisingour ofuse of lhis iufoma tion. This work ls publislied\rith the understindiry thal Mccrae Hill .nd ils .utho6 are supplyingiDibmutionbu1rfc not altcnpting10fcldcr cngiDccring or olhcr lrofcssionalscNiccs.If suchscNiccsrrc rcquircd,thc a$isrrnccof an rppropriatc shouldbc soughl. lroicssioDal

About theAuthor Harpril SinghSandhu,BSME, MSCerE.is the founderofRhino RobotsIDc..a nranu faclurerof bothrobotsandcomputernumeric-conlrolled machjncs,

CONTENTS Prefece

PART I The PIC i6FA7?A Chapter I An Introductlon to the PIC l6Fa77A Micrcconft!llor Unlt The Microconlroller 7 and Nol€sol Interosl 9 SpeclalPrecautlons DataSh€sls I SomeljseablePICS 11

3

Ch.ptor 2 Gettlng Started: The Hardware and Softwar€ Setup Th€ Programm€rc 14 Loadlngth€ Softwar€ 15 Uslngthe Sofiwarein lhe WindowsEnvironm€nl 15 ng Labs 18 SoftwaroNot6sfroml\,4lcroEnginee Chapter 3 lJnderat ndlng Mlcroohlp liEchnologyb plc l6Fa77A! A Descrlptlon ol the MCU 16F877Al\,4icroconlrolle/s Cor6Features 22 P€rlph€ral Fsatur€s 23 Conllguflng andControlling lhe Properties of the Porls PORTA 29 PORTB 30 PORTC 31 PORTD 32 PORTE 33 TIIVEFS 33

13

2l 29

Chapte.4 The Soflware, the Compilers, and the Editor The BasicCompilerInstruclion Set 35 The PICBASIC PROCornpiler Insiruction Sel 3z PICBASIC PFIOCompiler 42

35

Chapter 5 Controlling the Output and Reeding th6 Input General 47 ProgramsThal CreateOutput 48 Readlhe InpulsandThenProvideOulpul 48 ProgramsThal CreallngOutputs 48

47

vii

viii

colllEl{Ts

BlinkOneLED 50 BlinkEighlLEDSin Sequence 51 Dimand BrightenOne LED 52 LCDDisplay 53 Conlrolingthe DgiialandAnalogSetungs 56 to the LCD 56 Wling Binary,Hex,and DecimalValues andDisplaying the Besullson ihe LEDBarcraph 57 Readinga Potentiometer A SimpleBeep 60 an RC Servolromlhe Keyboard 63 AdvancedE)(ercise:Conlrollng Readng the Inputs 67 andDisplayKeyNumberon lhe LCD z3 FleadKeyboard and Displaylts 8-BitValueon LCDin Binary, ReadOne Potentiometer Hex,andDecimalNotalion,Alsolmpresslhe Binaryvalueon lhe Bargraph 74 76 andD splayTher Valueson the LCD ReadAl ThreePotentiometers Inlerlaces and ThalDelnesCompLrler Addinglhe Kindol Flexibility Adjushents 78 the Ablityto Makesophisilcaied Fleal-Time Dernonstrales Exercises 79

e3

Chapter 6 Timers and Counters General 83 Timers 84 Timerl:TheSscondTim€r 93 Timer2:The ThirdT mer 102 Counlers 104 ExercisesforTlmers112 Exercises ior Counl€fs 112 Chapter 7 Clocks, Memory and Sockets MernoryDevces SocketslJ3,U4,andU5:ForSerialOne-Wire WhlchEEPROIIITvoe ShouldYouUse? 115 SockelU3-l2C SEEPROM 115 SocketU4-SP| SEEPROIVI 1tZ Socketus-MicrowireDevices 118 SocketlJ6 Real-Tlme Clocks 120 The LTC1298 12-BitAlo-D CaryetletlAlsoUsedin SocketU6) SockeisU7 (andU8) 126 Chapter g Scrial Communications: Sockets lJg and UIO Whenand HowWillI Knowjl ll ls Working? lU Usingthe RS485Communicalions 137 Chapter 9 Using Liquid Cryslal Displays: An Extended Information Resource General 139 tjsingLCDSin YourPfojects 142 tjndetsiandng the Hardware andSoltwareInleraction 743 Talkingto ihe LCD 144

ll3 113

124 l3l

t39

CONTETS

lr

The Hardware 144 SettingOutOuf DesignIntent 146 Liquid-CrystalDisplayExercises 154

PART II The Prcjects Chapler lO

157

lJsing Sensors (Transducersl

Genera 159 The MoslBasicQueslionWe [,4ust Answer1s... 161 Typesoi Sensors 163 TwoInleresllng ResourcesYou W lWanllo Inveslgale

t59

164

Chapter I I Conditioning the Input Signal General 165 Allernaling CurrenlOutlne 166 Dir€clCurrenlOuune 166 SimpleSwitchesandolher conlacls 167 Circulry for Condilion ng dc Signals 169

165

Chapter 12 Conditioning the Output Slgnal Genoral 173

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Chapter l3 An Introduction to the Elghl Prolects TheWebSl€ 177 Ths EighlT€chniques 177 Notes 182

177

Chapter 14 The Universal Instrunenft A Background Discussion The Propedles andCapabilitjes oJa lJniversal Instrumenl 183 A BasicTemperalure-Controlling Device 184 Noles 186 Chapter 15 Counting Pulsesr A Programmable Tachometer Projecl1 187 Noleson UsingSeven'Segment Displays 199 Chapter 16 Crcating Accurat€ Iniervals with Timers: The Meirrnomes Prcjecl2 209 Iimefi 214 Timen 224 flmet2 228 rherlmet2Ptoyam 229 TheWalchdogTimer 230

183

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Chapter 17 Undetstanding the Counters: Counting Marbles 233 Prcie.13 Countingwllhan Escapement 240 Notes 243 SomeReal-World Counlng to a BegislerUsingan Inlerrupt 244 CounlingDirecilyintoan InlernalCounter 2.16 UsingTimerl ln Counlerl,lode 248 SpecialNoiesforTimerl Usage 256

233

Chapter lg A Dual Thermometer Instrument Ptoiect4 259

259

Chapter 19 An Artificial Horizon: A Table Suface Stays Level Projecl5 269 Discussion 220 Connscliofs 2zl SeltingUp lhe Hardware BuildingtheAnliclalHorizonTable 275 GravilySensorExercises 2zZ

Thal

Chapter 20 Bulldlng a Sinple Elght-Button Touch Panel Projecl6 279 Chapter 2l Single Set Point Controller with nemote fnhiblt Capability Prc)ecl7 293

269

279

295

Chapler 22 Logging Data trom a Solar Collector 301 ProjectI l,{icrocontrollerHardware344 Soitware 306

3Ol

Chapter 23 Debugging General 315 dndTroLbesSoolinql15 Deouggrng Cryslal That[,{usiBe Fixed:TheN,4icrocontroller FirsiProblem 316 NlustOscillale ll the ChipReluseslo Bun 318 io HelpDebuga Program 319 Usingthe PBPComplerCommands ThatCanPfovideDebugOulpullo a Se al Porl 319 Comrnands TerminalPrograms 319 DLrmb SolderlessBreadboards320 Level 320 Debugging ai the Practical and ReiatedNoies 324 lhe 16F877A Conliguring Seitngs 326 Contiguraton 326 Oplions 327 SimpleChecks 322

3t5

CONTET{TS ti

SomeProgrammer-Relaled Efforlvessages 328 ThingsI HaveNoticed bulHaveNolFigured Oui(andOtherl/ysteries) 328 Selting lhePots 329 Chapter 24 Some Real-World Proiecis You Can Build

331

Conclusion

335

Appendixes

337

Appendir A Setting Up a Compiler tor One"Keystrcke Operation

339

Appendix B Abbrcviations Used in thls Book and in th6 Datasheets

A41

Appendix C Lisiinga of PICBASICPRO Programs on th6 lntohot at melebs,co|n

345

Appendlx D Nole. on Dealgnlng a Slmple Battery Monitor fnstrument! Thinking about a Simplo Problom Out Loud

347

Appendlx E Ualng the Support Wob Sito to Help Make fnatrunents and Contlollers

349

Index

35t

PREFACE Theadventofthe miffoprocessor in a smallall-encompassing package andtheavailability ol easy-to-use softwarehavechangedthe scopeof whatcanbe easilyaccomplishedin the engineering laboratory andon the hobbyist'sworkbench. The pICo microcontrollenmanufacturedby Microchip Technology,lnc. of Tucson,Arizona form a formidablefamily of microcontrollers thatcanbeusedto fil1 myriadeveryday needs, I haveselected thisfamilyof mictocontrollers for theprojects in thisbookasa wayof introducing thenoviceengineering student, serious hobbyist, andprofessional technician to thebasictechniques thatmustbemastered |o usethesedevices to make fairlysophisticated instruments andcontrollers. Theprojectsin thistutorialhavebeendesigned sotheyeachemphasize theroleof one specifictechnique for usingthesemicrocontrollers. Together, theejghtprojectsgiveyou thebasicinformationandexperience yourequireto designandbuild the uniqueinstrumentsaddcontrollersyou will needfor bothyourspecialandeverydayneeds. Thebookis dividedinto two mainareasof interest.Thefirst partof thebookintroducesyouto thePIC 16F877A in somedetailsoyouknowwhatis available in these microprocessors in thewayof features. Thesecond partof thebookusesthesefeaturcsintheconstruction of theeightseparate projects in detail.Thel6F877Awas chosenasthelogicengineof choicein thatthis40-pinIC hasalmostall thefeatures one findsin theentirefamilyofMCUSin rheMicrochipTechnologies, Inc.offering.Once you understand you will be ableto usethe othermicrothe useof the 16F877A, processors madeby themandothermanufacturers withoutdifnculty.MicroEngine€ring Labs,Jameco,Solarboticsin Canada,and a largenumberof othervendors&lsoprovidea hostof boatdsonwhichthe16F877A canbemounted. TheLAB"XI boardmanufactured by microEngineering Labswaschosenasthebasic boardfor all theexperiments because it provides theuserwith a keyboad,an LCD displa$a piezospeaker,andthreepotentiometers alreadymountedon the boardand readyfor useaspartof theinstruments we will make,andit canbeusedasa rcliabletest pla$ormfor thesoftwarewe develop.It malces all theprojectseasierto assemble, experimentwith, andmodilyaswe developthem.Theprogransyoucreatecanbetransfened to othermicrocontrollers in thefamily,with nomodifications in somecasesandminimal modifications in others. All youhaveto dois tell thecompilerhowyouhavechangeal the wiring,identifythe microcontidleryou arcusing,andit doestherest.Migmtionto MCUSmadeby othermanufactuErs shouldnot presentmuchdimculryether If you know very litde aboutPIC mictocontrollersand haveneverplayedwirh them,I stronglyreconmendyou rcadmy first bookon microcontroilen,the Zr,rrr.ial aul ResourceBookfor th?L4B X1.This bookis availablefrom a numberof sources. includingme,microEngineering LabsintheU.S.,Jameco, Solarbotics in Canada, and ,lll

indcpcndentdistribubrsal1ovcr the $orld. Thc llrst haifof bolh booksaresimil.f in thal ftcy both concenlralcon lhe prolediesof thc nicrocontfoller.bul the first book lvill be mucheasierfor you i[]ou area norice.This sccondbook is targctcdat readeN who tind ny Tnotul a d Resourc?Book.l)r the LAB Xl too btNic for lbcir needs Thoughthis book covcls the b sic propcrticsofthe 16f877A. it doesnol li gcr on This lcxt delvesinlo advancedtechniqucs lirndamental expl.malionsand techniques. lbr thc advrrcedengirccr the univer grciltcf so is more suilablc integrutionand nd sily slLldcnl.the techniciln,andlhc amateufenginccr/hobbyist. (o rnrkc youxn expcnj nrichinehngurgcprogritnrming ol This booliis notciesigrl,rd gi!e to 11is dcsigned to preparcyolrto becont a lcohnicalcxJ)elton ['IC l ricioprcccsso|s. you n solidu dcKtandinsof lvhallhcsclogicalengine\cln do tbr you in fic l$out l/ llcld andto showyou how you crn usc(hcrn10do it. I will covcrcvefythingi r nonevcn so cwhal nontechniclllo n.rL.so if yotr halc a lrrininrnlLtndcr rnalhcnraticrl. (o andelcctRtlic.you canusclhcscrnicrocontrcllcrs ofthings bolh Incchanical slirnding I'RO using lhc PICBASIC i0 rnincl. I hrve conccrrtrirlcd on do usclulwork.Withthis ol-lhc borl(l lo gcne rle thc rlrscnrbly-lclci Couipilcf providcdby lhe InLrnulrclurc|ls il:rchinccodcnthcf thiu spcn(lliluc tcnchingyoLrhow lo usclNsenlblyhnguagc lhc .llld vcry Powcdll in thal il conpilor uscsu dirlcct oI BASIC lhrl is c.rsyto urxlcrslrrn(l irrgthc l)l(l urio()p()ccssors docsNcfylhing you nccrlLloncin lhc corrlcxlol-pr\)gfunrn is hothconlplLcl LrndliNl.Thclc fc tinrcswhclrrsscnllty liugLlrrgc Thc codcgcncflrLcd suhrl)u(irrcs canbc l(ldc(llo lhc p()grlnnmiuglo nrulicnrrosPccillllycilicrl trlskoxcctrlc () (io this.lhcconrpilcr irlk)wsil rn(lollofsllnrplcirllb n li( on lirslcr, andil yourrcc(l of lhc C' langurlgc. rhcsubjcc(.This workbookdocsnol covcrrsscurbl],lllngu.tgc 'l'hc sccon(lpn ol lhis book lcrrchciyou dboulbuildingbrsio nlicr1)conlrcllcr youhow lo buildcighlscParaLc dcviccs by showir)g nrrdcoDt()llofs basc(linsr|rrmcnLs i rd clch dcsigned lo hcll you(lcrlwilh tcal-wo d silulltions Thcsccightpfoiects.trc uscdto nlrkc cLrlllfollcfsltnd instl'tl on ()l)cilspcctol lhc LechDiqucs o|lc conccntlales mcnts.Scnsoftof vllious ki ds rrc ulilized lo scc holv thcy can bc trscdwith micra! contrcllcrs1ogct rhe rcsullsyou want.A detlilcd discussionof lhe pfolrlcnrqth.tl rvill be eDcountcrcd, anclholv they Draybc sol!cd, afe includcd. The workboLrksLar'rs out wifi thc constnrcliorof a Prcgr nrrnabletrlohorrolcrtll.l1 cotrnling lcchniquesusedin microprocess(ns: tcrchcsyou nboutlhc mos!fundamcDtrrl pulscs.lt nlsocolers thc Lrscof seven-segcnl displrys.so you $ill be coDrfort.lblc usirgthcmsincetheyar! usuallythebeslsolulionlb nininraldisplaysHrvingn:rs covercdin thiscxcrcisc.you will bc,rblcto inted ce lo all scnsoN/ ercd thc lcchniques sourcesthal prolidc pulsedsignals. The ability to rcid rcal-wofldinputsandcontrolfe.rl-workloutputsis conbincd 1(l lirst cfcatesimpleinlcraclions.andthennorc lophisticltedoncs.An enlite chaPlcris dcvolcdio feadinginput\ oi all kiods.In this chaptcr yor will lind tlc infofnadon nccdcdto intedaceyour MCt-lto the kindsoflhings you find in your hone rnd olice. as wcll asin theengirccrirg labofatofy.Both rc ,tnddc signalsarccorcrcd so you can bring thc infofrrationinto thc MCLJno maiter$hallhe source. Anothcr cntjfe chrpteris dclolcd !o contfolliDgoutpulsof rll kinds.The chapter givesyou |heinfbrmationyou needlC)controlthe realworld with .u MCU. Both lowsolid slatcswitchestrndrcla,vsarecolercd cunentTTL deviccsand high-cutTent

PREFACE

By the time you get to thc cnd 01 lhis book,you shouldbe able to usetheselogic enginesto createsnall ye1fairly sophislicalcdsystemsthat can do work that is bot! needed intcrestinganduseful.Frcm there,you will havetheknowlcdgcandconfidence norc complicated and sophisticated tasks. 10lakc on you will seethingsrcpealedfrom timc Sincethisbook is dcsigncdto be a resource, to time in nore than onc chaptcr This will saveyou from havingto read the crlirc book to get the iDfbmalion you nccd.By doiog this, eachchapterbasbeennadc ts selt'-contained as possible(wilhin reason).Scgmcnlsof code in the progmlnsalso repeatthenselvesfor the sime re son. A lot of what any inteiligentmlchine does has 1l] do with the softwafein the machinc.Thc softwarein the machineis speciJicto that nachiDc,but thc knowledge lhrlgocs inlo lhc dcsignofagood progfanris universal.Inthis book,wc will look into how the sollwareis dcsigncdlbr lhcscsma]lpmcessoll\.as well as how 10dclcrnrinc whxt musl be done lo makc a machincfunct;onprcpedy so it 0 0 molr complctcly realizeits potentii for doing useiirlwork. Plc miciocontrollers I sclcotcdthc Miflochip Technologyflmily of PIC nricroprocessorss the fbcusol thesenoloslbr lwo rcasons.First, MicrcchipTechDology providesihe mostoompfebensive lin lhc kindsof prqiectswe Iineol' nricroproccssors ploccssors providesalmostthe interlstcd in, lnd seoond, the coDrpiler lor lhese arc you ve h to do is lcll thc compilcf eDtircline ol PlCs with comprlhcnsivesuppo . AII which PIC you areusing,andil lhc lcaturcsyou havcbecnaddressirgin your prcjccl PlC. thc conrDilcrwill do thc rcst.Youwill nevcrhavcto arc vail$le on thal Darticular sivc M icIochip Technobgy buy anothercompilorif you staywith thc vcry oornprchcn tamilyof PICs. LabsLAB-Xl boad waspickcdasthe supporl The LAB-XI The microEngineerirg set of onboardleaturcslhat wjll lct boardbccnuscit providcsa very comprehensive us do itilllostall our softwareexperimentation anddevelopmenlon il wilh casc.The PIC l6F877A was choscnbccauscif hasalnrostall the featuresyou would cxpcctto All rhc skills you will developwith this deviccwill find on any smallmicrocontroller. be transferable to aDyolher systen you decidelC)lnigfaieto with ease.The boa and the compilertogeihergive you the most vdue lbr your invcstmcnt. ng Labs Discounted package Arrangemenhhavebeenmadewilh microEngincsrj packageof softwareand hardwafeitemssuilablclbr use to providea comprchcnsivc with this book it a discount.A couponto claim this discountis includedar the cnd ol

HARPRIT SINCH SANDHLJ

Chunpdisn, IL, U.S.A. and Internetsupporlsiles:wwwencodergeek.com wwwmhprcl-essional.com/sandhu

MAKINGPIC@ MIGROCONTROLLER INSTRUMENTS AND CONTROLLERS

AN INTRODUCTIONTO THE PIC 16F877A MICROCONTROLLERUNIT

Making Plc-based instrumentsandcontrollers hasto do with leaming how to combine the various capabilities that single-chip microcontroller units provide and utilizing a coherentset of interactive funclions that se e the purposeswe have in mind. A vast a[ray of PIC microcontrollers is manufacturedby the Microchip Technology Corporation of Tucson,Arizona. This tutorial is designedto introduce you to just orc of thesedevices-and do so ir a non-intimidatingway,if you are technicallyinclined but not necessarilyan electronic technicianor electrical engineer Getting to know this one d€vicewill exposeyou to most of the featuresprovidedin this entirefamily of devicesand makeyou comfortablewith selectingandusing the device that most closely meetsyour needs. The deviceI have selecledis the PIC 16F877Amicrocontroller.This is a 40-pin device that contains most of the featuresyou are litely to nnd in the family of microcontrollers that Microchip Technologymanufactures.In geneml,the salientfeatureswe needto get comfortable with can be describedas dealing with the lbllowing: : : I I I I t I

lnput capability Output capability Mathematical manipulationswifhin 8/16-bit math Using timers Usingcounters with digital andanalogdevices Commuoicanons Dealingwith displays Interacting with personalcomputers

The PIC 16F877Awill let us get familiar with all the precedingitems and more, andis an excellentchoicefor the first-tjmeserjoususer.This particularMCU (microAnumberofboardsthat controllerunit) is alsovery popularwithroboticenthusiasts. incorporatethis deviceare availablein the generalmarketplaceand on the Internet.

4

AI{ II{TFODUCTIOI{TO THE PIC I6FA77A MICROCOIITBOLLEB UNIT

As novices,if we want to get familiar with the conceptof building insfiuments and controllersbasedon PIC microprocessors,we needan easy{o-useyet sophisticatedand versalileboardto play with andtestour nascentideason-Though,ofcourse,it would be possibleto desigr andbuild a board that would do that, we do not havethe expedse or time at ihis juncture to do so.Therefore,I hale selectedthe very popularLAB-X I and the suppofting PICBASIC PRO Compiler software as the basic platfbms ior the proj' inthis book.Asyou readthistext,you will find thatfhesystem ectsandideaspresented provides an easy to useandversatrleplatform for checkingout your hardwarednd sofu ware ideasbefore commitling to personalcomputer(PC) boards,wire, and solder. McroEngineering Labs, Inc., the manufacturenof the LAB-XI board and the rclated PICBASICPROCompiler.mainoin a verylsetul andhelptul web sitethatwill bea tr€mendousaidto you asyoulean aboutyourLAB-XI in particular,andtheMicrochipTechnology CorporationPIC microcontrollen in general.Their Web site containsa large number of exampleprograms,tutorials,ando&er technicalinfomation to helpyougetstartedusingtheir boards.A largenumberof Intenet-basedWebsitesalsoexist,which ar€dedicaGdto the use of PIC microconlrollers.You shouldbooknark thosepertainingto your areaof interest. This resource supplementsthe i.formatjon on the Internet both from the microEngineedng Labs, Inc. site and from other sources.We will use the sampleprograms (modified for clarilication as may be necessaly)and other infonnation on the Web in your thisbook.This book providesextensivediagramsthatwill help you in d]Jsigning own devicesbasedon what you will learn.The diagramsar€ on the supportWeb site asAutoCAD files andcanbe expandedon for yourpafticulardesigns. There are rwo basic aspectsin iamiliarizing yourselfwith PIC microcontrollers-the hardwareaspectandthe softwa{easpect.The LAB Xl board is designedto Fovide you with thehardwarcpladbm you needto conductyorr first soitware(andhardware)experiments with PIC microcontrollers. The PICBASIC PRO Compiler provided by the manufactur€rsof the bodfd to programthe 16F877Aandsimilar microFocessors,is both easyto use andpowerful, and the code createdis fast andefficient- Other compilers are availablebut not coveredin this book. If you haveseriousbudgetconstmints,the softwareof choicefor usewith this boardis tl1esndler BasicConpiler lrom micmEngineedngLabs.This compileris avarlablefor about $100 (in 2008) andis not recorrnendedby me for seriouswork. (A free copy of the PBP compileris availableon themicrcEruineeringInbs Website,which containsall ihe insguctions in the full veNion ofPBP but is linited to 30lines of code.Even so.it canbe usedto for the effectivelytry out thepowerltl commandstructureof thelanguage.The insL"uctions languagecanbe dowdloadedftom themicroEngineeringLabsweb siteat no charge.Befor€ you mahea decisionin eitherd ection, be sureto try out the free versionof the compiler) On the other hand, if you have a seriousinterest in using PIC microconuollers, the compiler I recoDxnendis the PICBASIC PRO Compiler becauseit gives you the comprehensive powerandeaseof useyou needto do useful,eleryday,protbssionalwork rapidly. The PRO Compiler is available for about $250 (in 2008) and all the sotlware discussedin this workbook was written with the PICBASIC PRO Compiler in mind. A comparativelisting of the keylvordsprovidedwith eachcompileris pmvidedin Chapter4 on soltwarc and editors.

aN tNtRoDucttoN to tHE plc i6Fa77l [tcRocoltTRoLLEBuNtt

5

You will alsoneeda hardwareprogrannnerthatletsyou transferthe programsyou write on your PC royour PIC microcontrollerPrognmmersareavailableftom mjcroEngine€ring Labsfor theparallelport, theRS232sedalport, andtheUSB port of your computerThese programmersmrl€ it a "orc-button click pmposition" to transfer your program fmm your computerto the microcontmller andrur it without everhaving to removethe MCU from the board. (The USB programmeris recommendedby me.) The editing softwareneededto wdte andedit the programsbefore transferring them to lhe programmerand onto (hemioocontroller is a part of the compjler package.Other editors are available at no charge from a number of other supplie{s. None is a better choice than the editor provided. The salient hardwarefeatures(with somercpetition by categorieslisted) provided on the LAB-Xl areasfollows: The foliowing inp&tcapabilitiesareprovided: t I I : a I r r I I

A 16 switchkeypad A resetswitch Three potenliomete IR (infrared detectioncapability) (no detectorprovided) Tempemtulesensingsocket, (no IC provided) Real-time clock socket (no IC Fovided) Socketsfor experimentingwith tfuee basic styles of "one wire" memory chips Serial interface for RS232 (IC is provided) Serial interface for RS485 (no IC provided) PC board holesareprovided for otherfunctions. Seethe microEngineeringLabs, Inc.

The following or,tpul capabilifies are provided: r r I I I I I I

Ten-LED bargraphswith eight programmableLEDS 2line x 2o-characterLCD display module A piezo speakerAorn DTMF capability(digitaltonesusedby the phonecompany) PwM (pulse width modulation) for various expenments IR (infrared transmissioncapability) (no LED provided) Two hobby radio control servo connectors(no hobby servosprovided) Socketsfor experimenting with (also mentionedearlier) I Serialmemories : A to D conversionwith l2-bit resolution : Real time clocks The followlng I/O intefa.ss are provided:

t RS232 interface with lC I RS485 intedace, socket only (The chip is inexpensiveand easy to obtain.)

5

UN|t tO tHE PtC i6Fa77Ai|lCnOCO|{rnOLLEn At{ 0|TRODUCT|OI|

You can investigate the use of the following three r]ypesof Serial EEPROMS.

I lzc r SPI I Microwire The following n,ilcelldn€ors d€Iic€r are also provided: I A resetbutton I A s-volt regulator PIC 16F877AIC is not r A 40-pinZIF socketfor PIC microMCU (therecommended provided) I Ajumper selectableoscillator from 4 MHz to 20 MHz I An in-circuit progranming/debug connector : A prototyping areafor addilional circuilry I A l6-switchkeypad : A socketfor RS485 intedace (device not included) : A socketfor I2C serial EEPROM (device not included) I A socket for SPI serial EEPROM (device not included) I A socket for Microwire serial EEPROM (device not included) I A socket for real-time clock/serial aflalog to digital converter (devices not included) I A socketfor Dallas 1620/1820time and temperatureICs (devicesnot included) I An EPIC in-circuit progranming connectorfor serial, USB, or parallel Fogranrmer A11in all a very comp€hensive, well thought out, and useful experimentalpladorm suitable for our investigations. The board is available assembled,as a kit, or as a bare PCB. The board is 5.5 inch x 5.6 inch. Not all the featuresI have mentionedhereare completelyimplemented,but, as I stated,socketsor PC board pin holes are provided for all of them. You may not have to makeany solderingadditionsto the boardto usethe featurcsyou are interestedin, but you do have to purchasethe additionalIC chips ifyou are interested in their use. The standardversion of the board as shipped to you includes the following I The assembledboad I Software diskette r PDF schematicofLAB-Xl I Sampleprograns t Editor softwdre : Additional suppo( infomation (on the Web site) r (The 40-pin PIC nicrocontroller is not included.) I As received,the board is configured to run at 4 MHz.

IHE ItcnocoxtnofLER

TheMicrocontroller The PIC I 6F877Amicrocontroller(which is a necessary componenton the board)is not provided, becauseeach of the compatible PIC microprocessorsavailable have varying lbatures and you may want to select a unit that suits the application you have in mind.We will be usingthe reconrmended PIC 16F877Amicrocontrollerfor all our experiments.If you want to useanotherprocessol be sureto checkit for pin-to-pil com patibility with the LAB Xl board on the Web. Datasheetscan be downloaded for all the microcontrollers at no chargefrom the Intemet.A large numberof PICScanbe used in the LAB-X l. Seethe list at the endof rhischapter

IHE SOFTWARECOMPILEN The PICBASIC PRO BASIC softwarecompiler (ro be pwchasedseparately),produced by microEngineering Labs, offe$ the functions neededto control all aspectsof ihe hardwareprovided by Microchip Technology as a part of their large PIC offering. A11 the functions available on the PIC 16F8?7Amicroconfoller we will be using are acces sible from the software. The PICBASIC softwarc will createprograms ior almost the entire family of PIC microcontrollers. You will be able to usethis compiler lbr all your futue projectsif you stay with the Microchip MCUS. (It is, all in all, a very wofthwhile invesment.)

ADDITIOI{ALHARDWARE The following hardwarecan be addedwifhout making any modifications to the boad. Thesehardwareitems fit into socketsor onto pins that are provided on the LAB-XI as shipped.Not aI devicescanbe mountedsimultaneouslyin that someadalresses areshared by the socketsprovided. In our expedments,we will populate oily one empry socker at a time in order to make swe no conflicts arise. (There is no need to use more than one device simultaneouslyfor any one experiment,so this will not be a problem.) : Memory chips t I2C memory chip I SPI memory chip : Microwire memory chip | l2-bitA{o-D convenerchip

I Nru6355 I Real-timeclock chips r DSl202 r DSl302 r LIC1298 I Thermometer chip r DS1802

A

AlI II{TBODUCTIOI{TO THE PIC I6FA77A MICROCOI{TBOLIEBUN|r

Serialintedacechip I RS,l85 I RC servos(Two hobbyR/C servoscanbe controlledsimultaneously.) I The LAB Xl providcstwo sclsol pins for the R/C servos.A11standardmodelairclafl servoscanbeemployedandyou canuseeilheroncor lwo servos,(Usingthese is essentiallyanexercisein creatingpulsewidth modulaledsignalsandprotilesthat meetthe standards usedin the radiocontrolhobbyindustry.)

40-P|l{ DEVTCES in the40-pinZIF socket All40 pin MCUs ofered by Microchipcanbe accommodated prcvidedon rheboard.(Checkfor compatibilitywith the pin layoutbeforeselecting/ PIC l6F877Awe areLrsingis an buyingyowMCU. SeeFigure1.1.Therecommcndcd excellelt choicefor leaming.) BREADBOARDII{G

AI{D EXPAI{SION

All of d1eMCUS 40 pins (on the LAB-X 1) havebeenprovidedwith cxtra PCboardholes that can be usedto exiend the signals from thesepins to an oflboard location tbr turThe extensions areeasilymadewith standard0.1 inch on centcr therexperimentation. with matchins cables with henders. oins

1 2 3

40 39 38 37 36 35 34 33 32 31 30 29 2A 27 26 25 24 23 22 21

RA3/AN3/VREF 5 RA4/TOCKI 6 FA5/AN4/SS REO/RD/AN5 a 9 RE2/CS/AN7 1 0 VDD 1 1 VSS 1 2 oscl/cLKtN 1 3 OSCZCLKOUT BC0/T1S0S0/T1CKl1 5 RC1/r10StCCP2 1 6 RCZCCPl 1 7 RC3/SCK/SCL 1 8 19 20

BB7IPGD B86/PGC B85 RB4 RB3/PG[4 R82 FB1 FBO VDD

vss

RDs/PSP5 RC7/$qDT RC6/T)0CK RCs/SDO RC4/SDI/SDA RD2/PSP2

Ptcl6Fa77lA74

rlrfuiil&t:!;llaltPinout designarions for the 40-pin16F8774 PICmicroconlroller.

Asmall breadboard spaceis providedon rheLAB Xl itselfto allow the additionof a limited numberof hardwareiternsyou may needto experimentwith. Seethe supportWebsiteregardingthe availabilityof readynadeheadersandcables and so on, for usewirh the LAB-X l. (Theseare the devicesI neededandmadeup to allow me to experimentwith rhe l6F877Awhenrhecircuitrv I requiredwasnot avail_ ableon the LAB-X l.)

SpecialPrecautionsandNotes of Interest Thesecaveatscould havebeenplacedlater in this book but a(eincluded herero encour ageyou to think about the programmerbesrsuited to your needs. Pin 87 on the 16F877Ais connectedro a programmingpin on rhe EPIC parailcl plo_ grammerat all times,andthe programmerforcesthis pin high. ff you are usingthis pin in your exp€rimentand you decideit must be ,rlr, you must disconnectthe EPIC program_ mer to releasethispin. If you areusinga serialor USB programmer,it canbe lelt coDnected to the LAB-XI at all times.The major bcnefit of usjng theUSB or p,rallel programmerjs that it freesup your computer'sserialpot for cornrnunicationsto the LAB Xl. ResistorR17,which is connectedto the keypad,is ofno consequence to rhe opera_ tion of the LAB-XI. Ii is neededfbr some(pIC) pro$amming functionsand can be ignored(fbr ou. purposes).

DataSheets

The hardestpall ofleaming how to usethesemicrocont ollen is understandirgthe huee Srnceeirchddlarheet dararheet\. ,5similafbuldjFfer.nr r'om.,.n o,ne,drruitect.,i, lead\r(edlo'ele.Ioneurr\ornicfoconlroller.togcltlniliir;ilhundlhenusel; for all your inirial projecrs.ln this workbook, the two discussed/mentionedare the pIC l6F84A (|his chip will nor fit in the 40 pin sockerprovidedbur is a good alternare choicelbr thecost conscious), for yow smallprojects,andthepIC l6Fg77A.for larser more(omprehen\i!e projecl\.tach of lheceusesfld.hmetnuDandctn therctorc be proglammedover andover againwith your plogrammerand a prograrrming socket.The pocessor you selectwill be detemfuedby thekind ol VO andintemal featuresyou need, and the availabilityof inexpensiveOTp (onetime programmable) equivaientsifyou plan to go into producrion. A lot of the iniomation in the datasheets is morccomplicatedanddetailedthanwe needLoworry aboutat rhis lime, and we can do a lor of uselul work without under standingit in everydetail.Our main interesrjs in what the variousresistersare used for andhow lo u.e rhemprcperl).rndeffectivel)The limin! dirgram:rndotherdarc atnut thejnterl workingsofthe chipsarebeyondwhatwe needto undentandat the level of this resourcebook. Our inrerestis in beingabtero setrhevl]rious.egistersin the svstem

to

l{lcEocot{tRollEnu |T At{tNlhoDuctloNto THEPtc 16F87?A

so we can activate the featues we need for each particular project. Understandjng tiners and countersis a pal1 of this. The enlire interactioDoI the microcontroller with its environmentis determinedby the VO pins and how theyarc configured,so know Ingho$ tu conrigurc lheT/Oi\ \ef) impofldnr The datasheets are availableas PDF (pagedescriptionformat)files on the lnternet from the microEngineeringLabs Web site or from the Microchip TechnologyWeb site. Theseshouldbe downloadedontoyourcomputerfor immediateaccesswhenyou need them.Keepingawindowopenspesi{icallyfor thisdataisveryhandy.Evenso,you will "in you| hands." wart to prinr out someof the infomlationto haveit in thatwill supportour needsaslhey Of parlicularinterestaretheareasof &e datasheets applyto the following areas: and becomingfamiliar with what has alreadybeer definedby the : Undersianding Compiler software as il relatesto the software andnamingconventionsusedin the datasheet r Geftingfamiliar with the addressing the use of the varioLrs areasof memory on the MCU I Understanding yO pins to oru bestadvantage t Leaminghow to assignard usethe I Understandinghow to usethe PICBASIC PRO software eflectivcly r Getting familiar with the generalregister usageas it is implementedfor the control of the timers and counters

A FASTINTEN ET CONNECTIONIS PRETTY MUCH A MUST andil is veryhelpfulto havemore You absolutelyhaveto havean Intcmelconnection, than a standardphone line conneclion. so get the fastestconnectionyou can afford. You so nuch of the informationyou needis on theInternet.A needthe connectron because cable modemis stronglyrecommended.II you and a couple of neighborscan get together and folm a local areanetwork (LAN) and share a wireless modem set up, it becomesa reallyinexpensiveway to get fastInternetservice.The Wi-Fi signalshave no problemreachingall the apartmentsin a small building and sometimeseventhe house next door Relatively inexpensive amplifiers and repeatersare available to incleasc signalstrengthwherenecessary.

DOWNLOADII{GDATASHEEIS for ihe PIC16F87XA. Oneof rhe fi$t thingsyou needto downloadis thc datasheets You will, in ali probability,endup usingthe etaller andlessexpensivePIC 16F84A for a lot of your initial projects,so it might be bestto downloadthe iffolmalion fbr thatmicrocontrollerwhile you areaI it. As mentionedbefbre,thesefiles arc available from the Microchip Techrology Web site andthe information js free. However, thc two documentsconsistof about400pages,soyou probablywill not wantto prifit it all out ofthe morecommonlyusedinfonnationprinled You will, however,wantto havesoml3 The restshouldbe sloredon yourcomputer so you canreferto it whenevernecessary. so you car call up o( searchfor what you needwhennecessdry.

sotitEUSEABIE Prcs

tl

The Microchip Technology Coryoration Web site is www.microchip.com. Click "Support" on their Web site to find what you need.The items arc easyro download.Justfollow the instructionsprovidedon the site. ]lole Much oJthe infornation tou will needis provided on the Website that supports thb book. But eyen so,it can t rcpldce a.fast Intemet connectiotr.

SomeUseablePICS Thefollowing40-pinPICSwill workin theLAB Xl (asofJune2008).Orhersmaywork aswell. ChecktheseICs for thefeatuesyou needfor yourparricularapplication,and thenselecttheonethatprovides thebestmatch. Prc16C64(A), 16C65(B), 16C662, 16C67,16C74(AB), t6C765,r6c'7'7,r6c'7'74, t6F'71,16F'74'7,16F71, t6F'7'77,16F871, 16F874,16F874A,16F877,16F877A, 16F914,t6F9l7, t8C442,18C452,18F422, 18F4320. 18F4331, 18F4410, 18F.1.12. 18F1420, 18F4431, r 8F4439, 18F4455, I 8F448,I 8F4480, I 8F4510.18F45 15,18F452. 18F4520, 18F4525. 18F4539, 18F4550, 18F458.18F4580, 18F4585. 18F4610. 18F4620, r8F4680 Weareconsidering the 16F877A. The18F4331 familyoptimizes motioncontrolfor encoded motors. providedon eachMCU by thenanufacturervaryliom chipto chip.A chalt Features ofcomparative featuesis maintained by microEngineering LabsonrheirWebsite.

GETTINGSTARTED:THE HARDWARE AND SOFTWARESETUP

This chapterdeals with the minimum hardwareand software you need ro get starred. andwhatyou mustdo to setit up andgel it readyfor use. The following is a list ofthe hardwareneeded,andwhal comeswirh eachitem: I The LAB Xl board I Software diskette I Powersupplyfor LAB Xl I A wall-mounted ftansfbmer (9 to I 6 VDC at I amp) I USB port programmerfor the board (or other programmer.) : Software diskette t A l0-pin parallelcablewith 2 x 5 comectors(programmerto LAB-XI) ! USB cable from computer to programmer I Power supply for the programmer(not neededfor a USB programmer) I Wall mountedtransformer r A PIC l6F877A microcontroller or board-comparible40-pin MCU The following is a list ofthe softwarerequired: I PICBASICPRO Cornpiler I Microcode Studio editor software for writing the programs I Programmersoftware (comes\rrith the programner) The infomation neededis asfollows: I Datasheet for PIC l6F877A microcontroller(downloaded from the lntemet)

l3

ia

aND SOFTwanESEtuP GETflIO slARfED: rHE HABDWABE

Youshouldalreaalyhavethefollowing computorequipmed: r Wintel computer(IBM-PCor compatible) I Harddrive I Pdnter I Awindows operatingsystem connectionis recommended I Accessto theIntemet A broadband

Three programme$ are offerealby microEngineeringLabs One usesthe parallel port' ploone us;s tie USB poft, andthe third usesthe serial port. The operationofthe three use a We will is concemed) interface grammersis almo;t idenlical (as far as the user than to use is morc conveniert iJSB port programmerfor all o experimentsbecauseit the others sin-ceit does not neeala power supply.An impofant addedbonus is that if frees up the COM port for use with the computer (the parallel programmerallows this

I{OIES ON USII{GPROGRAMMERS It ge$itspower doesnotne€dapowersupplyorwalltransformer TheUSBprogrammer your port expenmentatron' for the senal port frees up USB ftomtheUSBport.Usinga which is impotant becausemost new computershaveonly oneserialpo(. The PC serial port connectsto ihe LAB Xl serial port for communication experiments For the serial po and parallel port programmers'first plug the 16-volt power cord connectorilto th! programner andthen into the wall socket The USB pro$alnmer also needsto be connectedbut doesnot needa power supply connection lfyou do nothave power to the programmerwhen you start the programming softwarc' the softwar-ewill not be able tosee the programmerand aII enor messagewill be displayed The softlqare will reDo( that it could not find the programmer It is iest to startthe progmmmersoftwarefrom the Mjcrocode Studio editor window proIf you aloit this way, the prc$ammer being usedis selectedautomatically and the automatically grarnyou are working on in the Micmcode ealitorwindow is transfefied io the compiler software and onto the MCU on the LAB-XI boad lt can be set up to "one mouseclick" operation see this book's Appendi\ A for more infbrmation be a Inse the microcontrollerinto the programmingsocketinrmediatelybefore you begu prcgranming the microcontroller (if you arc programming an MCU that is not on the Lai-xt;. ffri" appti""only ifyou areprogrammingaloosemiuoco roller Ifyou.ar-e programming a miirocontroller plugged into the LAB Xl, it can be Ieft in the board all pin itreiime. On1 orlly exception is for the parallel poft progftnmet beaausethe B? plan you lf is pulled low by this programmerandthus will interfere with your Fogram to usethis pin,'you musi unplug the programmerbetweenprogramming sessionsThis is mentionealagain as a reminder and caution-)

IISING THE SOFTWANE |l| IHE WII{DOWS EIIV|ROTTMEXI

The sequence to createa programinsidea microcontrolleris asfollows: l. 2, 3. 4.

Wdte the programin the Microcode Studioeditorenvironment. Compilethe program. Programthe device. Usethe dcvice. Steps2 to 4 canbe combinedinto onekeystrokc.SeeAppendixA.

Loadins the Software The following piecesof softwaF will be providedwith thevariouscomponentsyou acquire: t PICBASIC PRO Compllcr software and manual a USBPort Progrdmmel software and manual (or software for whateverprogrammer yolr decideto buy) , Microcode Studio(ll1eeditor) on disk or downloadedliom the Inrernet The DOS environmentis archaicandcanbe dif{icult for usersnot tamiliar with it. You do not have to deal with DOS to usc t}Ie hardwareand soflwarewe will use. Everything can be done from the Windows environment.Therelore. DO,Slrill 'lot re dircrs.red.Iiyou needto useDOS, a sectionat the beginningof the PICBASICpRO Compilermanualwilt tell you whatyou needto do. The first manualyou need to understandis the manualfor the PICBASIC pRO Compiler This manualcoverslrseof the sofrwarein the DOS environment.I suggest you ignore the first pagesof the manual and instead read the paragraph(below) thar I have written on how to tun everything under the Windows enviroffnent. Once yo are familiar with how the systemworks, you can go back andleam how to usethe software in theDOS environment. The DOS environmenr providesanumberofthings thatmay be uselirl, and you will want to know about rheseas you becomemore and more prc, ficientwith microcontrollers.

Usingthe Softwarein theWindows Environment The first questionthat needsto be answeredin almosrevery endeavoris always ,,Whar dolneed, whatdo I have1()do,andwhatwili it costto gerrhejob done?"Accordingly, we will addressthis now Let's assumeyou alreadyhave an IBM PC with a suitableWindows operaringsystem and that you know how to use it. Yollr computer needsthe lollowing capabilities to le1 you accessthe hardwareandsoilwareyou aregoing to useir with. In thjs book,I will

'I6

AIID SOFTWABE SETUE GETTIIIGSIARTEO:THEHARDWARE

dealexclusi,el!- trith the IBM-PC in awindows enrimtmenr. The softwareis not nvail ablefor the Macintosh.The foliowing outlineswhat you will need: only ! A3.5-inchfloppydrive(ifthe soflwareis providedon 1.4-MB3.5-inchfloppies yo (Incidentally, right). and you must read if off a diskctte for the system10work cannolcopy the softwareto a CD ROM andwork from there.It will not work for some software.)If the software is plovided on CD-ROM, you needa CD-ROM drive ! A hard disk with abolt 5 MB offree space.This is for softwarc storageand general and r A serialport (COM I or COM2) if you will be usingthe new serialprogrammer, programmer pol1 the USB ifyou will be using a USB board $195 I LAB-X I Experimenlers $10 N 16F877AMicrocontroller(nol partofLAB-Xl) $99 t USB programmer $250 ! PICBASICPRO Compiler ! Miscellaneous electronicitemslbr expcrimentation $100allowance At the e of lhis book thereis a discountvoucherfiom nicroEngineering Labs wolth about !j?0 off their rcrslope6 Bunllle. A desciption of what you get js included with the voucherYou haveto usethe actualvoucherin the book; a photocopywill not be acceptcd. The $ 100allowanceis for the sensors,servos,andothermiscellaneouselectroniccom_ ponents.It covers the needto purchasememory- ard time basedcomponentsthat are socketedibr, but are not provided asa part oi the needsmenlionedpreviously.You may decidethatyou do not needto expedmentwith theseat this time.The allowanceprovides for almost everything you need to experimentwith the LAB x I board. Labs,Inc.area numberol otherpreassembled Also providedby microEngineering boardsfor experimeriation and educatioml puryoses.They are listed next and may be in creating.All canbe used. morecloselysuitedto the insfiumentyou areinterested a r I r t t r

TheLAB X I ExperimdnreJ.'r,oa.l we are considedng. boardfor customcircuits. TheLAB X2 Experimenler's boardfor 20-pindevices. The LAB X20 Experimenter's boardlor 18 pin devices. The LAB 3 Experimenter's The LAB-4 Expedmenter'sboardfor 8 and l4-pin devioes. The LAB-XT Experimenter'sboard for telephonetechnology-relatedinvestigalions. boardforbuilding USB interfacesandperipherals The LAB-XUSB Expedmcnter's

In thisbook,t|e will considertheLAB-XI onlr.This boardprovidesa 2line by-20characterdisplay,which is very usefulin the leamingenvironmentinthatit canallow you 10seewhatis goirg on in the systemasyou experiment(ifyou programyour programsto displaythe appropriatcintbnnatioD). Startout by openinga newfolderon yourdesktopandlabclingitPIC Tools.Wewill store everythin? that has to do v,ith all our ptujects in this a efolder.We arc opening

USII{G THE SOFTWAREII{ IHE WIIIDOWS ENVIROI{ME T

17

this folder on the desktopnow buayou can move il to wherever you like in the future. Doing it this way avoids having to make a decisionas 1()whereto locaterhe foldet and the fblder is dght in front of you when you startyout computerand the deskop appears. Open tlle PIC Tools folder, and in it open folders-one for each of the items/ applications that wc are going lo be working with in this folder Name thesefolders

I ! r r

MicrcCodeStudio USB Prcgranrmer(or whichever unit you decide on) PICBASICPRO Compiler LAB-XI

Put the Microcode Studiodiskette/CDin the disk drive andopenit. Copy all files to the Microcode Studio folder Eject the diskette/CD and store it in a safe place. Put the progranmer diskette/CD in the disk drive and rcpeat the stepslisted previously for the software in this package.Repeatthe processfor all the diskette/CDs. Put a shotcut for the Microcode Studio program on your desktop.This is the only shotcut yon need when you \{ant 1l)createprogramsfor your MCUS. All other func tions of the systemcan be accessedfrom the window of this editor It's a good idea at this time to go to the microEngineering Web site and download the infomalion on the LAB-XI experimeDterboard, storing it iII your LAB-XI Tools fblder Useful exampleprogramsaboundin thesefiles andcutting andpastingfrom these to the programsyou are writing will sa\,eyou a lot of time. Theseprogramsare also on the book's suppoft Web site. ff you are familiar with and.hare infomntion lo I the Basi. Sam?, it would be a good ideato addtheseiiles to this file so all your microcontroller infomation is in oneplace. As a generalrule, you will never seethe compileras such.It is calledf.om rhe Microcode Studio editor screen,doesits work on compiling the program it is askedto compile, andthendisapp€arsinto thebackgroundreadyfor the next compilation request. The eflors displayedafter a compilation are generatedby the compiler If all goeswell, thercshouldbeno enorsandyou shouldgeta message tellingyou thecompilationwas successfullyperfomed. The new HEX file just generatedwill appearin the directory listing thenext time you opena file. The HEX nle will haveihe samenameasthe text file it wascompiledfrom. The PICBASICPRO Compilermmual covershow all this is donein moredetaill sourcenle HEXf,le

Unlltled.bas Unlitled.HEx

It should be noted that the HEX file is not createduntil all rhe slntax eno that the compilecanfind havebecnelimi atedby )ou. After a successfulcompilation ofthe code, there may still be errorsin the programming itself that will needto be addressedas you debugyour work.

'18

Tl{E HAnDI{AFEAl{D SOFn AnE SEIUP GEttlNG SIARTEOT

The adalressof the microEngineenngweb site is www melabscom/index htm If you have a CD-ROM burner on your computer (and if you do not' you should,get one), it is well woth youI tir\te to now copt the entire unadulteratedPIC Took folder data to o CD-ROM for safekeeping.Data on a CD-ROM is much more securethan the before on a floppy disk or disketio analthe best time to make a copy of it is right now you -aie any chang"s to any of the datayou receivedfiom the vendors ' For the purposesof generaldiscussionand expe mentation,we will always call the "Utttled", while the lext file that is the thtt x beingnanipulated .*ampL p-[ra body of the program vr'ill be called

This is tbe file the compiler compiles for the microconfoller you are using to oeate fhe HEX f,le it needs. The I{EX file createdfrom this program by the compiler will be referred 10as Uncr -fed. rlEX We do it this way becauseewry time Jou compiLeand 'att ctproqrun' the systemaulo'm.aticatly sawsth; prc|ram to disk at the sametime. This meansthat you lose the old program andcannoigo backlo it lf ) ou are\\ oru ng \ irh acomplicaledprogmm thi' lhererrc lol' olgood recson"lo go backto lhe $ ay .-"U..o*" u ,.ul ptoUt.mbecause things were. So, to;void this pitfall, every time you load a programfrom disk,/irst sale prcir as-Untitled.basand then play with it all you wanf Then. when you have a viable progBm dnd change ne{t cram,saveil to lhe namerhal is dpprcprialelor il Load lhe you ;is name to Untitled.bas and so on. I would even go so far as to recornmendthat 'flill be so that Blink bas saveeachversion of yoor prograrnwith a version designation"Blinkvl "Untiiled.bas,"and then re savedto disk as 0 bas''' while worked on as ''BlinkV|.0.bas would be \rorked on a\ "lJnlilledba- and then re sdvedd\ "Blinkv I . l.bas," and so on. Though sometedium is involved in doing this, I can assure you it will saveyou many headachesin the long rur' NolGe TheHEX fitescreatedbl the PBP compilen can be loaded into the PIC nicm' pngrammers contmllerc with other soll !1re/loaderslt is not imPeratire that hardware

SoftwareNotesfrom Labs MicroEngineering proThe following are somenoteslrom microEngineeringLabs regardingthe software videdby them: Labs t Locate the CDs labeled PICBASIC PRO Compiler and microEngineerinq

SOFTWAREI{OTES FROM MICROENGIIIEENI G LABS

t9

The compiler upgradeCD is identical to our full-version CD (with the exception of the red stamp).You can run ihc setup program to begin the installation process.It will install PBP and also ollers to install both MPLAB and Microcode Studio. The progranner CD is the samefor all the programmers.The sollwarc automatically findswhicheverprogrammeryou haveconnected. The LAB-XI materialscan be found on the PBP CD (uabx\LABxl) or on the LAB Xl productpageon our supportWcb site.A disk is no longershippedby microEngine€ring Labs with theXl. The compiler ships on CD with a printed manual. Besides the compilet the CD includesMPLAB (fron Microchip), Microcode Studio (ftom Mecanique),LAB-X andselected Plcmicro datasheets. sampleprogramsanddocumentation, All the programmers include software on CD. The meProg sollware is Labsprogrammerhardware. compatiblewith any microEngineering The LAB X boards include a schematic and brief description printed on paper as well as sampleprograms,applicabledatasheets,and details on their se. The latestcompiler (2.50) is shippedwith an enhancedversion tbat offers 32-bit long variablesdnd signed32-bit math operations. This is compatiblewith PICI8 series microcontrollers oniv.

UNDERSTANDINGMICROGHIP TECHNOLOGYSPIC 16F877A: A DESCRIPTIONOF THE MCU

PIC mioocontrollers are manufacturedby the Microchip TechDologyCorporatiofl of Chanaller,Arizona.The following addressandWeb sitemay be usedto contactMidtchip Technology.The Web site provides downloadsfor the datasheets. MicrochipTechnology CorporationInc. 2355WestChandlerBlvd. ChandlerArizona,USA 85224-6199

,480)/92-1/n (480)899-9210 FAX web site:wwwmicrochip-com

MicrcEngineedng l-abs,Inc.maintains averyusefulandhelpirl Websitethatwill alsobea tremendous aidto youasyoulearnaboutthePICmicrocontrole$by usingtheirLAB-XI. MicrcEngineeringlnbs Box60039 Colorado Springs, CO80960-0039

MicroEngineering Labs 1750BrantfeatherGrove Colomdo Springs, CO 80960

('7r9)5205323 ('7r9)5201867 e-mail:[email protected] Website:www.melabs.com/index.htm We will be using rftet6F877A Mictocontnller h Ihe LAB-X1 board.Not all the featuresdescribedin the 220 pagedatasheet of the l6F877Awillbe ad&essedjn the exercisesto follow, but enoughwill be discussedto give you the conlidenceand 2l

22

UiIDEBSIAI{DINGI{lCROClllP IECHI{OLOGYS PIC t6F6?74: A DESCnIPTIOI{OFIHE lilCu

youneedto proceed understanding onyourown.In moretechnical terms,t]risMCU hasthefollowingieatures

16F877 AMicrocontroller's CoreFeatures (Reducedfrom descriptions providedby MicrochipTechnology, Inc.) High pedbmance RISC CPU Operatingspeed:DC 20 MHz clockinput DC - 200 ns instructioncycle Up 108K x 14 wordsoI FLASH programmemory Up to 368 x 8 bytesof daramenory (RAM) Up to 256 x 8 bytes of EEPROM data memory Inlerrupt capabiliry Power-onreset(POR) Power-uptimer (PWRT)andoscillatorstart-uptimer (OST) Watchdoglimer (WDT) wilh its own on-chip RC Programmable code-proteclion PowersavingSLEEPmode Seleclableoscillatoroptions Low power high speedCMOS FLASH/EEPROM lechnology Fully staricdesign In CircuilSedalProg$nmingaICSP)\ ir twupin\ Single 5 volts In Circuil Serial Proganrming capability In-CircuitDeb ggingvia two pins Prooessor rea(Vwriteaccessto programmemory Wide operatingvoltagerange:2.0 volts to 5.5 volts High sinvsourcecuffent:25 milliamp Cornmercial and industdal lemperaturcranges Low-powerconsumption

PENIPHEBALFEATUFES

23

PeripheralFeatures The lbllowing arepefipheralfealuresofthc l6F877AMicrocoruollcr: with 8 bit prcscalar. s Tiner0: 8 bil timer/counter duringslcepvia vrith prcscalar(Il canbe incfemented a Timerl: 16 bit tinrer/countef an externalcryslal/clock.) with an 8-bii periodrcgistcr.prescrlar,andpostscalar x Tiner2: s-bil dmer/countcr e Two PWM modules(rnaximumresolutionis 10bils) a l0 bit multichannelanalogto digitalconverer serialpo( (SSP) a Synchronous asynchronous receiveftransmitter(USART) x Univcrsalsynchronous a Parallclslaveport (PSP)8 bits wide I Brown out dctcctioncircuitfyfor Brown out rcscl(BOR) you cando\\nload This MCU is dcscrjbedin pfofusedetailh a 220 pagedatasheet fron the MicrochipWebsiteat no charge.The datashcelis a PDF documcntthal yox shouldhaveavailablcto you at all iimes(maybe,elcn opcn.ir its own window.rcady thc l6FE77A.The sofiwarcyou for i mmediateaccess). whcncvcryouarcpfogramming nccdin ordertoread(butnotwrilc) PDFfilesis alsoavailablealnochargeon theWeb. You shouldhavea copy of the laleslvcrsion(9) of this very usciul softwarc(Adobe Reader)on your compuier in theseexercises. but thc mostcomWe will nol covcftheentiie220-pagedatashcc! thc oncsrelevantto theLAB X 1 andthose nonly usedlcaluresof theMCU (espe{-ially Aftefdoirg thc cxcrcises, andcontrollers)will bc djscussedneededfor our insLrumcnls you shouldbe comlbrlablcwith readingthe datasheel andlinding the infornalion ]'ou nccdto get youf wol'k done. ln our parlicularcase,on the LAB X I board,the MCU is alrcadyconnectedto the ilens on the borrd.Therefore.ifyou wal! to usethe LAB-XI lbr your own hafdwarc erperinents.you mlrslusethe MCU pins in a way that is compatiblewilh lhe componentsthatarealrcadyconneciedto ihem.Oflen (imcs.eventhougha pin is bcirg used in theLAB X1 circui!ry,you candrive somethingclscwith it wilhoutadlersclyaftect' ing your experiment(dcpcndingon the loadbeirg ,rddcd).The following is a list you canreferto in orderto quickly dclcnnineifthe pin 1dporl you \lant io useis tiee. or discovd how it is beingused.

PORTA

PIN*

USAGE

PINS PORTAHASONLYSX EXTEFNAL

PORTA.O 2

5K ohmPotentiomeier

POBTA,l

3

5K ohmPolenliomeler

L4emory chips

5

5K ohmPolentorneter

ljsed by clockchips,memory

PORTA-2 POBTA.3

24

UI{DEBSIAI{DINGltllCROCHlPIECHI{OIOGY'S PIC l6Fg77A: A DESCRIPIIOI{OF THE MCU

PORTA.4

6

Thisspecificpinhas needsl sPecialPull-uP

No analogiunclion

PORTA.s

7

chips Freefor Aio-D conversion l\4emory

PORTB.o

33

Keypadinputs

PORTB.I

34

Keypadinpuls

POBTB.2

35

Keypadlnputs

PORTB.3

36

Keypadinputs

PORTB.4

37

Keypadinputs

PORTB.s

38

Keypadinputs

PORTB.6

39

Keypadinplrls

Progfg device

PORTB.T

40

Keypadlnputs

Progagdevice

POnTC.0

15

Seruo/Clock

PORTC.I

16

Clockchips

PORTC.2

Plezospeakef

PORTC.S

17 '18

PORTC.4

23

chips usedwilh Nlemory

PORTC.s

24

Clockchips

memofychips A,/Dconversion,

PORTC.6

25

Transmltserial communicalions

R3232C

PORTC.T

26

Receivese al communications

RS232C

POnTD.0

19

LCDandLEDbargraph

PORTD.I

20

LCDandLEDbargraph

PORTD.2

21

LCDandLEDbargraph

PORTD.3

22

LCDandLEDbargraph

PORTD.4

27

LCDandLEDbargraph

PORTD.S

28

LCDandLEDbargaph

POFTD.6

29

LCDandLEDbargraph

PORTD.T

30

LCDandLEDbargraph

PORTE

PORTEHas Only3 ExlernalPins

POBTE.o

8

LCDwrtingconlrols

PORTE.I

I

LCDwfitingconlfols

PORTE.2

10

LCDwriiingcontrols

POBTB

Pro9agdevice

POBTC

Clockchips

HPW[,4 Memorychlps,servo/clock, IVemory chips,servo/clock

PORTD

Comnrunications

PERIPHERALFEATUFES

OlherPins Pn 1

IICLR l\,4icroprocessor fesetplnpull-up

Pin11

Vdd

Logicpower sVDC

Pin 12

vss

Logicground

Pin13

OSCI Oscillator

Pir 14 Pin31

OSC2 Oscillator Vss Logicgfound

Pin32

Vdd

Programming

Logicpower,5VDC

Re]istedin serialorder, the pinsare usedas followsi Pin1

tvtcLR

Processor reselpin,pullup Proglgdevce

Pin2

PORTA.o

5K ohmPolenlorneter0

Pin3

PORTA.I

5K ohmPolenlometer l

PORTA.2

A-lo-Dconv-orsions

PORTA.3

5K ohmPotenliometer2

ClockchipsU6

PORTA.4

Thisspecllicpinhas needsl specialpull-up

No analoglunction

Pin5 Pln6

PORTA-5 PlnI

PORTE,O

LCDwrillngconlrols

Pin9

PORTE.l

LCDwrillngconlrols

Pin10

POBTE.2

LCDwritlngcontros

oscl

Oscillator

OSC2

Oscillaior

Communications

Pinll Pit\12 P i nl 3 Pin15

PORTC.O

Pin16

PORTC.l

Clockchips

IVemory chips,servo/clock,

Clockchips

M€morychips,servo/cock

PORTC.2 Plnl8

PORTC.3

Pln19

PORTD,O LCDandLEDbargraph

Pln20

PORTD.l

LCDandLEDbargaph

P n21

POBTD,2

LCDandLEDbargraph

Pn22

PORTD.3

LCDandLEDbargraph

Pin23

PORTC,4

Usedwithl,4ernory chips

26

oF THEMcU MlcFocHlPIECH OIOGYSPlc i6Fa77ArA DESCRIPIIoN UNDEBSIAI{DING

Pin24

POBTC.5

Clockchips

Pin25

PORTC,6

Transmil seria communications

R5232C

Pin26

PORTC.T

Receiveseria comnrunications

as232C

Pln27

POBTD,4

LCDandLEDbarcraph

Pin28

POBTD.5

LCDandLEDbargraph

Pin29

PORTD,6

LCDandLEDbargraph

Pin30

PORTD.T

LCDandLEDbargraph

Pln31

Logrcgrouno

Pin32

Logrcpower feypadinputs

Pin33

PORTB,O

Pin34

PORTB,]

Pin35

PORTB.2

Pin36

PORTB.3

Pin37

PORTB.4

Keypadrnputs

Pin38

PORTB.5

Keypadinpuis

Pin39

PORTB.6

Progr'gdevice

Keypadinpuis

Pin40

PORTB.T

Proglgdevice

Keypadinpuls

Proglg device

Keypadinplrts

PORTB lincs set as inputscan be plrllcd up ioternally wi|h a soti\rare instruclion Inreffupiscanbc gcneraiedby changeson PORTBlineswhenlhey arcprogranned to

OFTHE PIC I6FA77A USIT{G THE A-TO-DCAPABILITIES wilh thc I-AB Xl boardby usingits You can makea numberol basicnreasurements The resolutionoI thc conveNioncanbc Il or analogto digitalconversioncapabilitics. 10 bits.Still highcrresolutionsareav.rilablei[ wc LrseICs thatgo in cnrptysocketU6. The measuremenls wc makecanbe usedto delernincthe foliowing: & & X e

Resistance Capacltance Voliage Frcquencl'(This is, ofcourse.not an.^-to-Dfunction.)

Resislanccis determinedby measuing how long it takesa rcsistorto discharyca is asaccuralcasthevalueof the capacitorthalhasjust beencharged.Themcasurement pafameters lnay nccd !o be adjusledin rc, lime to get a capacitorThe measurcmenl

PERIPHEBAL FEATUNES 27

{*${tlSitl:

A nearlyfull-sizeimaseof the versalileLAB-xl experl-

usablereading(meaningthe vaiue of the two componentsmust be selectedto get a reading in a reasonabletime with reasonableaccuracy). If the relative position of the wiper on a variable potentiometeris required, the A to D conversioncapabilitiesof the LAB-XI canbe usedto readthe potettiometerwiper position (not lhe resistance).The A-to-D converteralways measuresthe voltage across the device (hat you connectto the analoginput port. You have the choice of readingthe valueto a resolutionofeither 8 or 10bits. IJ you arereadingan 8 bit A to-D value,the value acrossthe resistanceis divided into 256 divisions andthe readingwill alwaysbe between 0 and 255 (inclusive).If you are doing a 10-bitA{o-D conversion,the valuewill be between0 and 1023(inclusive),but since1 byte canhold only 8 bits, the remaining2 bits mustbe readfiom anotherregister.This is explainedjn moredetailin the sectionon settingup A to D conversions for the IC in socketU6. Here,lefs tate a quick look at the POT command(used to read a potentiometer)to seehow this works. fhe POf Command The compiler provides the POT commandto make it easyto read the r€sistive load placed on a pin. ln order to usethis command,it is necessaryto setup the connectionto the LAB-X I asfollows:

26

plC 16FA77Ar OFTHEilCU A DESCRIPIION TECHNOLOGY'S G MICBOCHIP UNDEBSTANDI

Setup the pin usedon ihe MCU for analogmode Selectthe pin to be sedfor input Selectwhatthe excitationvoltagesoxrcewill bc (inlernalor erlcrnal) On rhe 16F877A.only l6 pinscanbe usedwith thePOTcommand,andthesel6 pirs havcbeenassignedlhe aliasesfrom PINo to PINI5 in thc lncludefile BSIDEFS-BAS (seethe PBP marual). For the 16F877A,theseare the pins on PORTB(0 to 7) and basedon theirpin counts PORTC(8 to 15).OtherPIC MCU havedillqent designations more information Seepagc 26 of the PICBAS]C PRO nanual for The POT commandis: POT Pin,

Scale, NUBR

P,, is thepir numbefqe hdrcbeendi.crs.ing forvariousRC constanls.IftheRC constantis large,thevalue S.?leis theadjustmcnt oI Scalesho ld be small.Scaleis detemincdexperimen|allywith a potenliometef thevalueofscaleshou]d in placeofthe resistiveload.At thelow endo[ theresistance, be 0, andat the high endil shouldbe255. NMrli is the variablelhc resultwill be placcdin. Valuesbelween5 and50K ohmsmay be readwith a 0.1 uF capacitor,as shownin the Conpiler manualunderthe POT command. Capacilancecan be measurcdby deternining how long i1 lakes to Capacitance chargea capacitorthroughan accuralelycalibratcdresistoror by scttingup an oscilla andncasuringthe oscillalorfrequency. tor with the two components yorfage Vollageis measured dividingnetworkwith preby settingup an appropriate resrslance cisionresistorsandmeasurirgthe vollageacrossan approprraie directly (asmadepossible Frequency The PIC 16F877Acan neasurctrequencies by thecompilersoftware).Thc timersandcounlcrswithin the MCU areusedto sctthe mcJ.urelrenr inlenaL\3nd(' 'unrin!\arJs."e. Ree.ting Siwitches Swilchescanbe readfrom thc lines of anyport setup asan input port.De-bouncjngmust be perlbrmcdeitherin hardwareor in soltwareto avoidlalse readlngs.(TheBUTTON comnandprovidesflexiblede bouncingcapabilities.) Make suretha!otherhardwarelhat may be connecledto the pins doesnot interlere with the switchlunctionandiis detection. Switches armngedin a matrix can be read by set Peading Switches in a iltatix dng andreadingihe rows andcolumN in thc matrix.The techniqueactivalesonerow ofbutlonsat a time by makingit high or low andthenseeingiI anyof thecolumnshave beenaffected.A detaileddesciptionofhow this is doneis in Chapler5.

FORIA

29

Configuringand Controlling the Propertiesof the Pofts The PIC 16F877Aprovides 33 VO pins distributed acrossfive porls. Each of the ports hasuniquecapabilitiesbuilt into it. The following sectionof this book discussesthe capa_ bilitiesof eachof the pots with specialattentionto thesepropeties. Thesedescriptionsare cufsory and are designedto provide a quick and ready reference.Refer to the actualdatasheetfor detailedinfomalion on thesepolls. The dalasheet provides information at a level lhat cannotbe provided in a short introductory text like this. Refenhg to the datasheetsfrequently will make you comfortable with them in a shorttime.

PORTA PORTA is a 6 bit wide bidirectional port with both analogand digital capability Note The general rule is that ifa PIC de\)ice hasany analog inputs built into it, it will come up as an analog input.lerice on resetdntuor staftup. The PIC 16F877Ahasanalogcapabilityon PORTA(andPORTE)so it comesup as an analogdevice on statup and rcset. lf you are going to use it as a digital device, you must set registerADCON as needed.The most common \alne is ADCONI to q.0000A111for vsirg the LCD display. This line of code will be seenin nany of the setsall the analog programsin tlis book and is explainedin Chapter5- (7o00000111 pinsto digital,but therearemanyotherchoices.) The PIC 16F87?Asupportsexternalaccess|o only six of the eightpinson this port. loadEachof the six pins may be setto functionasan input or outputby appropriately "0" (zero) in a bit in this register setsthe cofesponding pin ing the TRISA register A "1" (one) setsit to function as an input. to function as an output, while a Thus,selting... IRIsA=%o0U1000 thisbookbecause (% mcansthisis a binarynumbelWowilt usethisbinarynotationthroughout bh, is on fte Bil7. the mosl significant it makesit easier to seewhateacbbit is beingseito. is on theright.) ieftibit0, theleaslsignificant. WouldmakelinesA0, A I , andA2 outputsandlinesA3, A4, andA5 inputs.Themost sienifcant 2 bits are igtrr,'ed (and could be set to I s or 0s) becausePORTA has only andtheycanbe six activelines.(However,the 2 ignoredbitsareusedby theprocessor for specific You shouldnot set them.Again, seelhe datasheet readwhen necessary. details.) As mentionedearlier, the specilic functions (the usesthe pins are put to) of the pins are controlled with the ADCONI (the first A-to-D CONtrcl) rcgister

30

OFTHEiilCu PICi6Fa7?A:A DESCBIPIIOI{ iECH||O!OGY'S IVIICROCHIP U DERSIAI{Dn{G

All the pins haveTTL level inputsandfull CMOS level outputdrivers.This makes il casy to connecl theselines direclly to standardlogic components(meaningthat r,t&dlh no intermediatercsistors are needcdbetweencomponentsif TTL or CMOS com ponentsareinterconnected). PORTA(tetisnations are somewhatcomplicated.PinsA0, A 1, A2, A3 ' (skip A4)' and Pin A5 canbe configuredas analoginpulsby settingrheADCONI registerappropri_ ately.Pin A3 is also usedas a voltageinput fbr comparingwith the analogvoltage inputson otherpins.Pin PORTA4,is usedasinput for the timerTIMERo.lt is called ToCKlforTimer0clocklnput.ThisisPin6oflhcPlCandisusedastheinputpjnlor TIMERo only whenconfiguredas such.It is a Schmitttriggerinput with opendrain ourput.Opendrain meansit actslike the contactsof a liny relay Scbmitttrjggeredinputs betweenstatechanges) of the hystelesis haveincreasednoiseimmunity (becausc TRISA and ADCONI PORIA arc registers that control The two ADCON1 controlstheA to-D and voltagereferencefunctjonsof PORTA The set jn ting of thevadousbits selectacomplicatedsetofconditioN thataredescribed detail whenADCONl andin thisbook.(Inlhcprecedingdiscussjon, in atablein thedatasheet this feature.) we wereaccessing wassetto 7.00000111, PitrA4 hdsspecielneedswhenuseAas an output.lt canbepulleddownlow but will fioat when serhigh. lt must be pulled up with a ( LoK to I 00K) resislor to tie it high when This pin hasan opendrajn outputratherthar the usualbipolarstate this is necessary. pins. As notedearliet this pin is skippedin the A-to-D conversiontable. of the other (Ignoringthisfact is a sourceolmany commonmistakes,so keepthis in mind.)

PORTB PORTBis a full 8 bjt-widebidireclionalpo|t. Intcmalcircuitry(meaningbuilt into the MCU) allowsall the pins on PORTBto be pulled up to a high slate (very weakly) by setting pin 7 of t}le option register at iDputsareaffected.Thesepull (OPTION REG.?)to 0. Only thosepins designated ups are disabledon starlup and on reset. Pins83. 86. and87 areusealfor the low voltageprogramningofthe PlC. Bit 3 in TRISB mustbe cleared(set|o 0 or pulleddown to 0) to negatethe pull up on this pin fbr more to allow programningto take place.Seepages42 and 142in the datasheet infomation regarding thc 93 pin. This is wry inportant. Pins84 to B? will causean intefupt 10occurwhen lhcir statechangcsif they are configuredasinputs andthe appropriateirltelTuptsareconfigured.Any of thesefour pins that are conligured as outputswill be excludedfiom the intelrupt leature Thc intenxpts are controlled by the INTCON (interupt control) register.This PORTB interupt capa bility hasthe specialfeatureoflelting it be usedto awalen a sleepingMCU. Pin B0 has spccjal inteffupi functions that are controlled tbrough the INTEDG bit' which is bit 6 of the OPTION-REG. See datashectfor more intbrmation rrt?/dl interrup arc nuted tu the PIC throughthispin.Extemal inteffuptsarethosethatare createdbv eventsoutsidethe PIC MCU.

to8Tc

3i

The three registersthat conuol PORTB are TRISB, INTCON, and OPTION-REC. OPIION-REG controls t]le oplional functions of PORTB as follows. a I r r t r I :

Bit B0 of OPTION_REG setsprescalarvalue BitBI ofOPTION REG setsprescalarvalue BitB2 of OPTION REG setsprescalarvalue option(usedin low-voltagepogramming) Bit83ofOPTION REG setstheprescalar Bir B4 of OPTION REG setsTimef0 input pulse edge selection Bit B5 ofOPIION REG setsthe clock selection Bit B6 of OPTION REG setsedge selectionfor interupts (progranming uses) Bit 87 of OPTION-REG setsthe pull-ups when cleared (programming uses)

PORTC PORTCis a full s-bilwide bidirectionalpoft. Al1 the pins on PORTChave Schmitttrigger input bulTers.This meansthey are designedto be more inrmune to noise on theseinput lines. The altemate function of the PORTC pins are defined as fbllows: r BitC0 rBitCl r ! r I a r

BitC2 Bit C3 Bit C4 Bit C5 Bit C6 Bit C7

VOpinorTimerl Oscillatoroutputor Timerl Clock input VO pin orTimerl Oscillatorinput or Capture2 input or Compare2 output or Hardware PWM2 output yO pin or Caprure1 input or CompareI output or HardwarePwM I output yO pin or Synchronous clockfor bothSPI andI2C memorymodes I/O pin or SPI dataor dataI/O for I2C mode VO pin or Synclronousserialport dataouQut clock transmitol synchronous VO pin or USARTAsynchronous VO pin or USART Asynchronousreceive or synchronousdata

Specialcaremust be takenwhen using PORTC'Sspecialfunction capabilities,in that someof ttrcsefunctions will change/setthe yO statusof certain other pins when in use, and this can causeunfbreseencomplications in the function of other capabilities. See for details. thedatasheet The rcgister that controlsPORTC is the TRISC register.No other registersare involved. DEFINES are usedto set or contlol ce{ain PORTC functions. Nole Thespeakeron the IAB-XI board is con ectedto pin C I , so the useof this pin is linited becdusethe noise generatedby the speakeri)hen this pin is usedcan be very iffitating to humans.Sincethis is one of the lines that allotrs the generatiottof contin' uous backgroundPWM signals (HPWM 2), it compromisesthe clean use of this pin unlessthe speakeris remo|ed or the siSnal is put thmuqh a gate to clean it up. (l rcc' ommendthat Jou avoid modifcations to the boa l if )ou ca .) The load of the ti ) speakerloaclsthepin and can compromiseceftain other uses,but in ost casesyou can

32

UNDERSTATIDITIG MIChOCHIFIECHI{OIOGY S PIC l6F677A: A DESCFIPTIOI{OF tHE MCU

se this?in witlloutcancem.(Utulercertain situations,theJie(tuencJon thili pin can be sethieh enoughto be abovehLnan heatingrunge,allo\,)ingthepin to be usedLike

PORTD PORTDis a full s-bilwide bidirectionalporl. All the pins on PORTD have Sshmiutrigger input bullers. This mcansthey are designedto be moreimmuneto noiseon the inpurlines. PORTD can also be configuredas a microprocessorport by settingPSPMODE throughsettingTRISE.4to 1. (Notethatwe arespecifyingbil 4 of PORTEhercinter nally; lhereis no extemalpin4.) In this odc.all lhe input pinsarein TTL mode.(See page48 of the datasheet.) The alterrate function of the PORTD pins arc delined as lbllowsl Bit D0 or parallelslaveport bit 0 Bit Dl or parallelslavcport bit 1 Bjt D2 orparallelslaveport bit 2 Bit D3 orparallelslavepoft bit 3

PortD is lhe

Bit D4 or parallelslavepolt bit4

parallclslaveport

Bit D5 orparallelslaveport bit 5 Bir D6 or parallelslaveport bit 6 Bit D7 or parallelslavepoll bit 7 The registersihat controlPORID areTRISD andTRISE.TRISE controlsthe operationof thePORTDparallelslaveport modewher Bit TRISE.4is sel10l. (Rcmember againthatonly pins E0, El, andE2 areavailableexternalto theMCU on PORTE.) Slaveporrfunctionsas setby PORTEwhenBitTRISE.4 is set1()1 are: Bit TRISE.0dircctioncontrolofPin PORTE.o/ RD /AN5 Bit TRISE.I directioncontrolof Pin PORIE.I / WR /AN6 Bit TRISE.2directioncontrolof Pin PORTE.2/ CS /AN7 BilTRISE.3, NOT USED Bit TRISE.,ISlavepoft select

l=Slaveport selected =Useas slandardl/O port

Bit TRISE.5Bufferoverfiowdetect

l=Write occurredbeforereadingold dala o=No effor occufed

IIMEBS

Bit TRISE.6Bufferstatus

33

1=Stillholdsword o=Hasbeenread

Bit TRISE.TInputbufferstatus

1=Full O=Nothingreceived

Readthe datasheeta coupleof limes to get a betterunderstandingof theseoperations. The precedhg is a very bdef ovefliew and is intendedonly to alet you and gjve you an idea of what the possibilities are.

PORTE PORTE is only 3 extemal bits wide and is a bidjrectional poll. The oiher bits are internal andareusedasmentiooedearlierunderPORTD (to which they arerelated).AII externairhreepin' canalsobe u\eda\ analoginpul\. All thepins on PORTEhav€ Schmittirigger input buffers when usedasdigital inputs. The altematefunction of the PORTE pins dre dennedas follows: Pin REo direction control of Ph PORTE.0/ RD / AN5 Pin RE1 direclior control of Pin PORTE.I / WR / AN6 Pin RE2 direction control of Pin PORTE.2/ CS / AN7

TIMERS The PIC 16F877AMCU has four timers: a 'vafchdogtimer and thr€e regular timers. Theseallow the accuratetiming (andcounting) of chronologicalevents.Timers arediscussedin much g&ater detail in chapter 6. with t}Iemthat can be Someof the timershave(pre- andpost) scalarsassociated youcan imagine,the scalusedtomultiply the timer settingby an integeramount.As ing ability is not adequateto allow all timed inte als to be created.We also must considerthe unce(ainty in the frequencyof the clocking crystal,which is usually not exactly what it is statedto be (and may drift with ambienttemperature)This meansthat though fairly accuratetimings can be achievedwith the hardwareas received,additionalsoftwareadjustnentsmay have to be addedif more accurate resultsaredesired.This is doneby havingthe softwaremakea correctionto the time every so often, (This also meanstiat an extemalsource,that is at leastas accurate as the resultwe want,is neededto verify the timing accuracyofthe devicecreated) As always,the three limers in fhe microconfoller are clocked $ a fourth of the oscillator speed,meaningthat a timer within a 4 MHz systemclock gets a counting signal at I MHz

3a

uNDEBStAilOll{GlllCROCHlp IEGHIIOLOGVSPIC I6FA77A: A DESCRIPTIOIIOF tHE ISCU

Very simply stated,an 8 bit limer will count up to 255 and then flip to zero and start counting from 0 to 255 again.An intenupt occuls (a bit is set) every time the timer rcgister overflows from 255 to 0. We respondto the interupt by doing whateverneedsto be done in responseto the interrupt and then resetting the intefupt flag bit (to 0). On timers that pemit the useof a prescalat the,prescalarlets us increasethe time between intenupts by mulliplying the time betweenjnterrupts by a definable value in a 2 , 3 , or 4-bit location. On timers that canbe wdlten to, we can startthe counterwhereverwe like (to changethe inteffupt timing), and on timers that can be read, we can read the contentswheneverwe wantto. Example:A l-secondtimer settingwith a prescalarsetto 16 would provideus with an interupt every I6 seconds,andwe would have 16 secondsto do whaleverwe wanted to do betweenthe interrupts or we would miss the next interlupt. If we neededan inlenupt every 14.5seconds,we would usea timer setto 0.5 seconds and a prescalarof 29 if 29 was specifiable(which it is noo. So not all time intervals can be createdwith this strategybecausethere are limits as to what can be put in the timer and what can be put in the prescalarwhen we are using 8/16 bit rcgisters and specific oscillatorspeeds.

WATCHDOGTIMER A watchdogtimer is a timer that setsan inteffuptwhenit runsout so as to tell us the program has hung up or gone awry for some reason.As such, it is expectedthat in a properly writtel program, the watchdogtimer wi]l never setan intemrpt. This is accomplished by resetiirg the watchdog timer every so often within the program. The compiler doesthis automaticallyif the watchdoglimer option is set.Setting the option does not guaranteea programthat cannothmg up. software erro$ andinlinite loops that reset the timer within them canstill causehangups.

PRESCALARSAI{D POSTSCALARS The value of the scalingfactor that will be appliedto the timer is determinedby the con tents of2 or 3 bits in the intenupt control register.Thesebits multiply the time between inteffupts often by powers of two. Prcscalarsand postscalarshave the sameeffect on the interrupts: They delay them.

COUNTERS OnlyTimer0andTimerlcanbeusedascounters. Timer2cannotbeusedasa counter becauseit doesnot have an extemal input line. Both the timers andthe countersar€coveredin detail in Chapter 6.

THE SOFTWARE,THE COMPILERS,

AND THE EDITOR

MicroEngircering Labs, Inc. provides h'roBASIC compile,'sthat make wdting the code for the PIC family ofmicrocontrollers offered by Microchip Technologytremendously easy.In this book, we will discussthe more powedul of the two: the PICBASIC PRO Compiler A listing of the conmands provided by eachcompiler is provided in the fol lowing to let you compale tt€ tw., compilers and selectthe one best suitedto both your budget and yout needs.

TheBasicCompilerInstructionSet The following is the smaller compiler of the two:

ASM,.ENDASM

Insert assemblylanguagecode section.

BRANCH

computedCOTO (equivalentto ON..GOTO).

BUTTON

De bounce and auto-repeatinput on specifiedpin.

CALL

Call assemblylanguagesubroutine.

EEPROM

Defirc initial contentsof on-chip EEPROM.

END

Stop execution and enter low power mode,

FOR..NEXT

Repeatedlyexecutestatement(s).

GOSUB

Call BASIC subroutineat specifiedlabel.

GOTO

Continue execution at specifiedlabel.

35

36

THE SOFTWAhE.IHE COIPIIENs. AIID THE EDTON

HIGH

Make pin output high.

I2CIN

Readbytes from I2C devtce.

I2COUT

Sendbytes to I2C device.

IF.THEN - GOTO

If specifiedconditionis true.

INPUT

Make pin an input.

ILETI

Assign result of an expressionto a variable

LOOKDOWN

Searchtable lbr value.

LOOKUP

Fetch value from table

LOW

Make pin output low

NAP

for shoftperiodoftime. Powerdownprocessor

OI-ITPI-IT

Make pin an output.

PAUSE

Delay (l msecresolution).

PEEK

Readbyte from register

POKE

Write byte to register.

POT

Readpotentiometeron specinedpin.

PULSIN

Measurepuisewidth (10 psecresolution).

PULSOUT

Gercratepulse(10 Llsecresolution).

PwM

output puise width modulatedpulse train to pin

RANDOM

Generatepseudorandomnumber

READ

Readbyte fiom on chip EEPROM.

RETURN

Continueexecutionat statementfollowing last execuled GOSUBcall.

REVERSE

Make output pin an iryut or an input pin an oulput.

SERIN

serialinput (8N1). Asynchronous

SEROUT

serialoutput(8Nl). Asynchronous

SLEEP

Power down processorfor a period of time (l secresolution).

SOUND

Generatetoneor whitenoiseon specifiedpin

TOGGLE

MaIe pin output and toggle state.

WRITE

Write byte to on chip EEPROM.

tHE P|CBAS|C PROCOflPllEn NSlRUCtlOll SET

l7

MATH OPERATIONS All math operationsare unsignedand performed with 16-bit precision: Addition Subtraction Multiplication MSB of multiplication Division Remainder MIN

Minimum

MAX

Maximum

&

BitwiseAND BitwiseOR BitwiseXOR

u

Bitwise ANID NOT Bitwise OR NOT BitwiseXOR NOT

ThePICBASICPROCompiler InstructionSet This is the larger compile. of the twol @

Inset one line of assemblylanguagecode.

ADCIN

Readon chip analogto digital conveter.

ASM..ENDASM

Insertassemblylanguagecodesection.

BRANCH

ComputedGOTO (equivalent to ON.-GOTO).

BRANCHL

Branchout of page(long BRANCH).

BUTTON

De-bounceand auto-repeatirput on specified pin.

CALL

Call assemblylanguagesubroutine.

CLEAR

Zerc all variables.

3A

flIE SOFTWANE. IE COIIIPILEFS,AI{D IHE ED|ION

CLEARWDT

Clear (tickle) watchdog timer.

COUNT

Count number of pulseson a pin.

DATA

Define initial contentsof on-chip EEPROM.

DEBUG

Asynchronousseflal output to fixed pin and baud.

DEBUGIN

Asynchronousserial input from fixed pin and baud.

DISABLE

DisableON DEBUG andON INTERRLIPTFocessing.

DISABLEDEBUG

DisableON DEBUG processilg.

DISABLE INTERRUPI

Disable ON INTERRUPI Focessing.

DTMFOI-IT

Producetouch{ones on a pin.

EEPROM

Define initial contentsof on-chip EEPROM.

ENABLE

EnableONDEBUG andONINTERRLlPTpocessing.

ENABLE DEBUG

EnableON DEBUG processing.

ENABLE INTERRUPI

Enable ON INTERRUPT processing.

END

Stop execution and enter low power mode.

ERASECODE

Eraseblock oicode memoty.

FOR..NEXT

Repeatedlyexecutestatements.

FREQOUT

Produceup to two frequencieson a pin.

GOSUB

Call BASIC subrouti e at specifiedlabel.

GOTO

Continue execution at specifiedlabel.

HIGH

Make pin outpot high.

IIPWM

Output hardwarc pulse width modulated pulse train.

HSERIN

Hardware asynchronousserial input.

HSERIN2

Hardware asynchronousserial input, secondport.

HSEROUT

Hatrdwarcasynchonous serial output.

HSEROUT2

Hardware asynchronousserial output, secondport.

I2CREAD

Readfrom I2C device.

I2CWRIIE

write to I2C devlce.

IR.THEN..ELSE..ENDIF

Conditionallyexecutestatements.

INPUT

MaIe pin aII input.

LCDIN

Readfrom LCD RAM.

tt{E ptcBAstc DRo co ptLEn |l|stnucflolt

sEt

36

LCDOUT

Displaycharacters on LCD.

{LET}

Assignresultofan expression to a variable.

LOOKDOWN

Searchconstanttablefor value.

LOOKDOWN2

Searchconstant/ variabletablefor value.

LOOKIIP

Fetchconstantvalueftom table.

LOOKUP2

Fetchconstant/ variablevaluefrom table.

LOW

Makepin outputlow

NAP

Powerdownprccessorfor sho periodof time.

ON DEBUG

ExecuteBASIC debugmonitor

ONINTERRUPT

Execute BASICsubrootine on anintenupt.

OWIN

input One-wire

OWOUT

one-wireoutput.

OUTPUT

Makepin anoutput.

PAUSE

Delay(l msecresolution).

PAUSEUS

Delay(1 psecr€solution).

PEEK

Readbytefrom register

PEEKCODE

Readbytefrom codespace

POKE

Writebyteto register

POKECODE

Wdteto codespaceat deviceprogranrming time.

POT

Readpotentiometer on specifiedpin.

PULSIN

pulsewidthona pin. Measure

PULSOUT

pulseto apin. Cenemte

PWM

Outputpulsewidth modulatedpulsetrain to pin.

RANDOM

pseudorandom Generate number.

RCTIME

Measurepulsewidth on a pin.

READ

Readbytefrom on chipEEPROM.

READCODE

Readwordfrom codememory.

REPEAT..UNTIL

Executesta(ements until conditionis true.

RESUME

Continueexecutionafterinterrupthandling.

RETURN

Continueat statement following lastGOSIJBcall.

40

AI{DIHE EDITOB THECOIIIPIIEBS. THESOFIWABE.

REVERSE

Make outputpin an input,or an input pin an output

SELECT CASE

Comparea vadable with different values'

SERIN

serialinput (BS1 style)' Asyncbronous

SERIN2

Asynchronousserial input (BS2 style)'

SEROTIT

Asynchronousserial output (BS I styl€)'

SEROUT2

senaloutput(BS2 style) Asynchronous

SHIFTIN

serialinputSynchronous

SHIFTOUT

Slarchronousserial output

SLEEP

Powel down prccessorfor a period of time'

SOUND

toneor white noiseon specifiedpin' Generate

STOP

StoPProgramexecutron'

SWAP

Exchangethe valuesof two variables

TOCGLE

Make pin output and toggle slate'

USBIN

USB input.

USBINIT

InitializeUSB.

USBOUT

USB output

WHILE..WEND

while conditionis rue' Executestatements

WRITE

Wrile byte ro on-chip EEPROM'

WRITECODE

Wrile wod to code memorv'

XIN

X-10 input.

XOI-IT

X-10 output.

IIIATHFUNCTIONS/ OPERATORS The mathoperationsareunsignedandperformedwith 16 bit precisjon: +

Addition

-

Subtraction

*

MultiPlication

**

Top 16 bits oimultiplication

+/

Middle 16bits of multiplicalion

/

Division

tHE P|CBAS|C PFOCOflPtLEn StnUCTtOt{SEt

4r

Remainder(modulus) Shift left Shift right

ABS

cos

Cosine

DCD

2n decode

DIG

Digit

DIV32

31 bit x 15-bitdivide

MAX

Maximum

MIN

Minimum

NCD

Encode

REV

Reversebits

SIN

Sine

SQR

Squareroot

&

BitwiseAND

I

Bitwise OR Bitwise exclusiveOR BitwiseNOT

&/

BitwiseNOT AND BitwiseNOT OR BitwiseNOT exclusiveOR

As can be seenflom the precedingcomparison,the PICBASIC PRO Conpikr prryidesa muchmoreconprchensbe instruction set and.thereforeis the compiler of choice fbr seriousdevelopmentwork. It is, of course.alsopossibleto programmicrocontrollersin assemblylanguageand"C," but lhis book doesnot cover theseianguages.A numberof good books are availableon the subjecr,and somethat I iooked over are listed jn a file on the suppo{ Web site with my cornments.Someeducatorsfeel that a Junior Collegelevel classon the subjectis the bestway to leam how to do this and thereis somemerit to this but for our purposesthe PICBASIC PRO Conpiler will do everything we needard is much easierto use. In addition to the compile\ Wu need an editor lo allow you to write and edit programs with ease.A very adequateeditor is provided as a part of the compiler package. Its calledtheMicrocodeStudioeditor.This comprehensive andpowerfuleditorisaiso availableat no charge(on the Internet)from Microcode Studios.This is a completeeditor

42

ANDTHEEOIIOF COMP|IENS, THESOFTWABE.IHE

with no limit on the numberoilines of codeyou can wrile. It is fully inlegratedwith the software and hardware Fovided by microEngineering Labs and is the editor of choicefor mosluscrs.(Thefreevclsionis limiled to compilingFogramsforjust a few ^nd the 16F814) bul theseincludeboththe -16F877A microcontrollers. Threeofthe editorsavailableare: : Midocode Studio Mecanique'sMicrocode Studiois a powedul, visual,inte grateddevelopmentenvironment(IDE) with an ln-Circuil Debugging(ICD) capaLabs'PICBASICPRO Compiler bility designedspecificallylor microEngineering at no chafgc.The only limilation from the Inlemet This softwarecanbe dow oaded you to run only one IDE at one time-This is not a on the softwde is thal it allows realhandicapat our lcvel of interesl,howevet sinceit is theeditorthatbestsuilsour needs,andbecauseall programsin lhis book werewrittcn with this edjtor r Pmton+ Lite BASIC editor (providedby Crownhill) This is a tesl version oftheir editor and is limited to 50 lincs of code and threeprocessors(includingthe PIC 16F877A).Ilyoulike thiseditot you canusethisasyournain editordndthencutand pasteto the Microcode Studio to compile andrun your programs'andthus go around the soljine limil. The ndrive ldnguageof this editot ir t?ott e r.,ne ds PICBASI C, so thereare other handicapsto contendwith- (Theseincompatibilities are best avoided-) r Miqochip MPLAB This is the sotlware that the makef of the microcontrollers' Microchip TechnologyInc., providesfbr cditing programswritten for their PIC serics It is an assemblylevcl programmerWe will not be doing any of microcontrollers. progra ming, b l the editotcanbe usciul. language assembly

PROCompiler PICBASIC The PICBASIC PRO Compiler-hereaftcrreferredto as the PBP providesall the functionsneededto programalmostthe entire family of PIC microconuollersin a BASIC-like environment.This meansii allows you to wite ptogramsthat readthe inputsandwrite to theoutputsina simpleandeasyto-learnfashionlt meansthatcommunicationsare simplifiedand that the time ii takesto get aII applicationrunningis reducealmanyfold.lt also meansthat the programsare easier10 follow and debug (thoughdebuggingcangetquilecomplicatedevenon theseseeminglysimpledeviccs). The compilersuppots only integermath,but that is not a big handicapwhenwe are working with theselimited microprocessols It alsomeansthat the programsthat aredevelopedareshorterthanassemblylanguage programs, but they are slower in their execution than assemblylanguageprograms (Complications alsoexistthathaveto do with the useof inteflupts,andwhich mustbe addressed,but theseare beyond the scopeof this book ) All the exercisesandexamplesprovjdedin the text arebasedon the PBPcompiler' We will,rdt go overthe detailedinstructionsfor usingeachofthe PBPinstructionsin the soitware the text.It is expectedandwill be assumedthatyou will havepurchased

ptcBAsrcDno coflDtlEn

andthuswillhave themanualfor thecompiler in hand.However,somecommandscan be complicated to implement and so we will spendtime on them as necessary. The compiler is kept cunent by miuoEngineering l-abs. fbr the latestMCUS rcleased by MicrochipTechnology. TheLAB-XI usesthe 16F877AMCU, andit is theMCU of choice,thoughot}er MCUS that have a generalpin-for-pincompatibililywith this MCU may also be used.Al1 the experimentsand exercisesin this book will useihe PIC 16F877Aonly. The compiler addressesalmost all the capabilities of this MCU, and we will cover the useof all the devjcesprovided on the LAB-X I board to developthe comforl level you needto incorporatethem into your instrumentsafld contro]lers. Detailedinstructionslor installing the softwareon your PC arcprcvidedin the compiler manual.It is not necessaryto install the softwarefrom a DOS prcmpt. It is mucheasierto install it underMndows with the ' Install.exe"or equivalentfile providedjn eachpackage. The softwarecan be set up so that "one mouseclick" will transferthe program liom the editor to the PIC microcontroller andrun the programin the PIC. In oder to do this, you have to add a couple of functional codes to the programner operating system. Thesecodestell the programmerto load the prcgram and executeit. Installing the soft ware is covered in detail in the chapteron gefting stafted.

A SIIiIPLEEXAIIIPLEPROGRAMUSII{GPICBASIC A program that makes the LEDS blink ON and OFF is usudlly the first program written by beginners.The pupose of the programis not to blink the LEDSbut ratherto allow you to go through the programming proceduresin a simple and straightforward way, and get a result that is easyto verify. Onceyou have the LEDSblinking, you will know you havefollowed all the stepsnecessaryto write and executea program, Larget morc complicatedprograms may be m ch more difficult to write and debugbut they are no moredifficult to compile,load,andrun. Progmm4.1 outlinesthe keystrokesfor writing andnnning tlle "blin}" the LEDSprogramin PICBASIC. 1i!aii0a!i!1{i!i

Therlrst program(Blinkins alleishiLEDSon PORTDoneai a tlme) nyBtinkSleds . BAS Harpri! Singh Sandhu Copyriqht o 2008 A11 Riqhts Reserved 1 / F e b /2 0 A B 1.Q

CI;EAR DEFINE OgC 4 I.ED ID VAR BYTE t VIR BYTE

, clear FnM nenory , define the osc freq ouE !!e two d..lablec LfD ID and t ; as 8 bi! bytes

44

ANDTHEEDITOB COMPILENS. IHE SOFTWAEE.IHE

alleighiLEDSon PORTDoneai a llme) tii.!!!.iia!ii.,:a!ii Thefirst program(Blinking outputs

TRISD =%00000000

s e t P O R T DL o a l l

UAINI"OOP:

toop is eaecuLed forever the counter to I initiaLize Lhe I LEDS do it for puLs nunber ln PoRTD pause so you can see the displav by 2 noves Llr LED Left I pos nultiptying go up and increnent counter do it alr forever FND statement always end tith

FOR LED,ID

= I TO a

PAUSE 100 l = I * 2 NEXI I,ED_ID

coEo lrArr{LooP END

PICBASICPBO TIPS AND CAUTIONS l. To getcontexlsensitivehelp,movethe cuisorovera PICBASICcommand,click to setthe culsor,.mdPressFl. 2, Programsassumethe PIC is running at 4 MH4 To changethe default setting (for l3xample,to 20 MHz), simply add DEFINE OSC 20 at the top of your program and se! the oscillatorjumpe$ on the LAB X I accordingly lt is good praclice to always specily the oscillator speealin a program.Beginne$ shouldstartwith 4 MHz designs Th" LAB-XI i. ."t up to run at 4 MHz asreceivedfrom the factory' Seethe manual' The definedOSC speedhasto match the hardwareorystal for ihe hardwareand sofl rn'lruclion' u r-relo \^orkconeLtl\.This i. e\peciall)imporlanllor rrme-'en5ili\e be set (to must ADCON1 the LAB-XI' 3. Before you can use the LcDisptay on pause 500 msec you about must 11to nake PORTEtandPORTAIdigital) and 7o000001 not rced a You may 10allow the LCD to siafl up before issuing it its nrst command rnsfuc pause,orasho er pausemaybe specilied,if therearemanytime_consuming tioft beforethe lirst LCDOUT inslruction is executed (Other valuesofADCONI can also be used,dependingon how you want the A and E porls coniigured Seeihe discussionin ChapterI8.) throughoutthis bookto sctrelevantbytes binarynotation(7,01010101) 4, I haveuseal and registersso you can teadily seewhich bit is being set to what.The compiler acceptshexadecimaland decimal notalionjust as willjngly Binaty nolation doesnot permita spaceafterthe 7osign,andall eigbtbits mustbe specilied. 5. When using Wod ior prografiming support,if a single quotation mark (') is copied f.om a Word fi le andpastedinto the Microcode Sludio editot it will be i nterpretedas a (') andwil thel€fore,1rrpnperlr stut1the commensecrio, of the line All thesehave to be changedin the ealitorafter pasting.Paslingfrom the editorsil1lo Word doesnot exhibit fie sameeffect. lf you use(:) for ihe conments' this problem doesnot occur 6. All the namedregisterscanbe calledby namewhenusingthe compiler'The rcgisler namesare the sameas thoseused (defined) by the manufacturerin the datasheet and are the sameacrossthe entire family of PIC microcontrollers if they provide thc ol lowercasenamescanbc used Thc DEFINESm st be samefunction.Uppercase

PtcBAStCPnOCOi|PLER

4!

stated in uppercaseonly, and the spellings in the DEFINE lines are not always checkedby the compilerl Therefore,be very careful with the spellings when adding DEFINES to your Fogram. 7. Circuits and segmentsof circuits areprovided tbroughoutthis book to showyou how to connect up the hardwarewhen you designyour own circuits. If you have access to AutoCAD, you can cur and pastethe diagramsin the files on the suppo Web sire intoyourown designs. All rhediagrams in rhi( bookareon rheWeb"ite.

A FREE DEMO BASIC COMPILER A free version of the PICBASIC PRO Compiler by microEngircering Labs can also be downloadedfrom the miuoEngineeritg Labs Web site. This is a fully functional com_ piler with the limitation that pro$ams are lmited to 30 lines of code. This is enough lo allowyouto le\t rhecompiler andanyinsruclionlhat) ou migh(ha!ea special inl;_ est in. This version can give you a good idea of the power and easeof use of the lan_ guage.I encourageyou to try out this compiler beforeyou mate your compiler pulchase.

CONTROLLING THE OUTPUT AND READINGTHE INPUT

General Alter all is said and done, itt abour the input and output, and what happensbetween the two of them. It has to do with how we use the many capabilities piovided within eachPICA4CU, and how creative we are aboutusing thosecapabilities.In this chapter we sta leaming to use allthe input and output capabilities Fovided on the l6FgtTA usingLAB-XI. . All the programswe will be discussjngare provided on the supportWeb site rwwwencodergee k.com,. $ hichjr mrintained aspanof rhi"book.Simlly narigareto your areaol intetest on the Web site. You cancopy the liles from rheWebsireandrun rhemon rhe 16F877Ain the LAB_XI. The eiercises listed in each chapter are exercisesthat are designedto increaseyour familiarity andcompetencewith the 16F8?7A.The answeisto them arc not Drovide;_ Tnpreparation .et up $e L AB X I so ir canbe prolrarned wirh tor wriringprograms. one_mouse bunonclicl or b] prc.cingFt0. asdescribed in derajtin App;dix A ot lhis The yO that usesICs in the sevenempty socketson the LAB_XI boatd is covered sepantely in Chapters7 and 8. Thesechaptersalsocover one_wirememory.A-to D con_ vefler..anda numbefol relaledthermometric de\ ices, The VO that usesthe sedal po{ (as RS-232 or RS485) is covercdin Chaprer8. This covers commrmicationsbetweenpICs and personalcomputers, Wewill leamaboutinpurandoulputb) fir,rq ritingri;ple progfams tharconrrol fie outputs,and then wrire prcgramsthat read ihe inputs.We will leam how to contlol the outputsfust, becausethis canbe donedirecily from the sofh{arewithout needfor anv inpul.Once$econtrol lbeourpur.we $ ill ledrnho$ lo rcddlhe inpulsanJ mdke!h; outputsrespondto them in a useful and coherentmanner The following is a list of the prcgramsto be developed.

THEIIIPUT ANDNEADING THEOUTPUT COI{TSOLLIIIG

The oulput is what we are iooking for in anyinsllument lt is the final resultof all the work we do.We will interactwithall of theoutputdeviccson theLAB-XI in theseprogrums.

BASIC PROGRAMS t , t ! t ! !

write a program to conlrol one LED on the bargraph Controlall eightLEDSin the bdrgraphconsecutively Dim andbrightenoneLED (creatingpulsesof variouslength9 Wite 'Hello world" to the LCD on its lwo lines Wrirc binafy anddecimalvalucsto the LCD. Outputa sinple tonc on the speaker Outpura telephone|onesignalon the speaker

ADVANCEDPROGBAM ! Move an WC sc o baok and lbfth

ProgramsThatReadtheInPuts andThen ProvideOutput l. Write a simpleprogramto readthe lirst colunrn,Iirst row bulton' andtum ON one LED while the buttonis down. 2. Rcadthe enlirckeyborrdanddisplaythc binaiy valueofthe row andcolumnread on the LCD. 3. Readthe kelboatd anddisplaydecimalkey numberon the LCD anddisplayits S_bilvalueon thc LCD in binaty,hex, and 4. Readonepotentiometer decimalnotation.Also displaythebinaryvalueon thebargraph anddisplaytheirvalueson the LCD5. Readall threepotentiometers 6. Advancedr Use the tfuee potentiomctersto control an R/C scrvo Conrol the loca tion of the centerposition,the limit position of the endpositions,andthe rale of movemcnl. Usethrcc switcheson the keyboardto move thc servoclockwise'centerthe servo,andmovc i! conDterclockwise.

CreatingOutputs we cando this wilh pto_ k willbc easierif wc learnto conlrolthe outputsfirst because or input signal we hardware any additional gramsthat we write without lhe need for thetwo line LCD, proceed control of to the will stdrtwith the simplecontrolofLEDS.

CFEATII{G OUTPUTS 49

which is providedon rheLAB-XI, andthenmoveon ro usingthe speakeranalan R/C hobbyservo. Lefs startwith tlrc standard"luming an LED ON and OFF, program.We will use one of the LEDSin the ren LED bargraphtharis providedon the LAB,XI. We have control of only the eight righlrnosrLEDSon this bargraph.The lefmost LED is thc power ON indicatorand the one rcxr to it cones ON if we were using a commoncalhocle affangementfor the bargraph(asopposedto the commonanodean aigemen! asit is cur rently configured). Thc cirouitrywe areinrerestcdin is shownin Figure5.1.AI othercircuitry of the LAB X I is still in place,but we havesuppressed ir sowe arenot distracted by it andcan concentrateon the LED that is of interestto us. (PORTD.o).PORTD.0 refers to bit 0 oI PORTD. In our lirst exercise,we want ro control rhe rightmosr LED of the LED array.This is connectedto bit 0 of PORTDin the circuirryshowDin Figure5.L Our progran needs to tum this LED ON ard OFF !o demonstrale tharwe havecomplereconrrolof rhese

5 3

io

15

Flgurc 5.t

26

The LEDbargraphchcuilryfor POBTDpin O.

q6

.r'N-rROLLlxG THE OUTPU-IAND NEADIiIGTHE INPUT

ln general,the ports on the microcontrollers(MCUS) aredesignedso they can be used as inputsor asoutputs,In fact, the portscanbe programmedso celtainpins on a po are inputs and others are outputs.All we have to do is lell the program what we want doneandthe compiler will handlethe details.The compiler not only allows you to define how you will usethe pins of eachport, it can alsosetthem up as inputsor as outputs automatically,dependingon the instructionsyou useto addressthe pin in your program. You have a choice of setting PORTD to an output port and then setting pin I on this ponhigh, or you cansimplytell the compilertomakepin 1 of PORTDhigh andit will take care of the setting up details. The portscanbe treatcdjust like any othermemorylocationin the microcontroller' andmanipulatlons usethemin calculations By name,you canreadthem,setthem,aLnd location.lfthingsarecon_ just like you canwith anyothernamedorunnamedmemory nectedto the po s and pins, ihe program will interact with, and respond1o,whatever is connectedto them. (Any namedport, register,or pin canbe addresseddirectly by name for all purposeswhen using the PBP Compiler They are called out as they are named in the datasheetfor eachindividual PIC by lhe manufacturer)

Blink OneLED Type the following program(Prognm5.1) into yourPC and saveit lt doesnotneecl to be savedin the samedirectoryas t}Ie PBPexe program.To keep with the conventionsbeingusedin the compilermanual,call this programmyBLINK.BAS so it doesnot overwritethe BLINK.BAS programprovidedon the disk thal camewith the LAB Xl. The program to control pin 0 of PORTD is as fbllows: an LED[Weare usinslhe controlling(blinking)an LED(Blinking lliP$iim$lll LEDon the bargraphl) rightmost CLEJAR DEFINE

clear

nenory LocaLions

OgC {

nooP: HIGE PORTD. O PAUSE 500 IJO!' PORTD. O PAUSE 500 GOIO LOOP END

lurns LED connecled Lo D0 oN deLay 0.5 seconds turns LED connecled to D0 oFF delay 0.5 seconds qro back to Loop and repeat operation aL1 prograns nust end with END

The program demonstratesthe most elementarycontrol we have over an output: that of turning it ON and OFF In this program, we did not have to set the port directions (with theTRIS conmand), becausethe HIGH andLow commandtale careof that aulo matically. (If we usedPORTD.0=I insteadol HIGH PORTD.0, we would have had to

BLINKEIGHILEDSl|{ SEOUET{CE 5l

SetTRISDto %l1111110fi$r to setall lines1()inputsexceprD0. whichis shownasrhe only pin setto bc an outpur.) We will uscbinarynotation('/.11110000) for settingall pins,pors, port directions, and rcgistervaluesthro ghoutthis book, thoughyou can usehexadecimal($F0) and decimal (DEC 240) notation interchangeably.Using bindr.ynorarionlets you seewhat eachpin i\ doilg wIhoul hr!ing ln m"le .rn)co ref.ior\.

Blink Ei t LEDsin S uence IDProgram5-2,we blintrtheeightrightmostLEDSon thebargraph,oneLED aratime. The circujtrywe areusingfor this progran is shownin Figule5.2.We do this by set ting PORTDto I andthenmultiplyingil by two a toralof eighttimesto movethelighrcd LED left onepositionin eachiteration.Norerhatthe lastmultiplicarionovcrflowsthe ll bit counterandturnsall thc LEDSOFF

tMac-''@l

:r :il

::r ::3

-

:

=

LEDbargraphchcuihy to all of PORTD.

52

CO TNOLIINGTI'IEOUTPUTANDREADITGTHE INPUI

,t:1 .ji6!iil:5;2:l

Blinkingeighl LEDSone aller lhe otheron a bargraph

CLEAR DEFIAIE OSC 4 LED-ID VA.R BYTE A VTR BYTE TRISD =%00000000

calL ouL the two variables s e r P o R T Dt o a 1 L o u r p u r s this loop is executed forever initialize Lhe counter to 1 do it for the I LEDS puts nunDer a. PURrU pause so you can see the display I-ED left nuLtipLy by 2 noves liL

IIAINLOOP: F o R t E D t D = 1 T O I PORTD=A PAUSE 1OO

1

go up and increnent counter do it aLl forever always end with END

NEXT IJED ID GO!!O MAIIIITOOP END

Dim andBrishtenOneLED by larying |hc abilityto dim anLED (at PORTD.O) In Program 5.3,we demonstrate thedutycycleofthe ON signalto theLED. il thiswavleis Turnson an LEDanddimstheonenextto it (Doing tlB!!0iai!.riltqiSil youcompare thebrightness ofthetwoLEDS) '.

CLEAR DEFINE OSC 4 ERISD = %11111100 X VAR BYTE

I.OOP: FOR x = 1 TO 255 SIEP PIIM PORTD. O, X, 3 PAUSE 200 /X NEXT X GOIO LOOP END

ri

5

d

-LEaD

>"of605.

set only PoRTD pin 0 and 1 to outpuLs decLarexasavariable turned PORTD.I ON & conpare io PoRTD.o

2

set up foop foi x vary Lhe duty cycLe pauses longer for the dimer values en.f of Loop for x reLurn and do i! again all progxans Fith an END statenent

With the precedingprograms,we learnedthatwe cancontroltheON OFF staieanci the brightnesson an LED. Controllingthe brighhesswill becomerelevan!when we areconrolljng sevensegmenldisplaysbecausethe LEDSin them dretuned ON one display at a time andthc duty cyclehasto be managedpfoperly10get an acceptable

LCD DISPLAY

53

I.CD Display Thesenotesdescdbethe useof, and interactionswith, exisringhardwarecoonections10 the liquid crystal display as it comeswired on the LAB-XI module.Thescconnections are defined in the program with DEFINE staiemenrs.Define thcm as necessaryin your designs, keeping in mind thaldesignsthatfollow theconnections lbr LAB-X I will allow you to usethe LAB Xl as the testplatform.(Evenil your designis subsrantially dif ferentfrom the LAB Xl circuitry,this willrenain ausefulfeaturefor resringthe LCD andcertainI/O lhatmay be the same.) On theLAB X1, theLCD datais fed from PORTD,andall 8 birsofthis port arecon necled to the LCD. It is controlled trom the 3 bits of PORTD. You theretbrc have the choiceofusing onlythe4 highbitsor PORTDasa 4-birdarapaihfor rheLCD orusing all S bits.The entireport is alsoconnectedto eighrofthe LEDSon the ten-lightLED bargraph.(The two leitmost LEDS in the bargrapharc uscd 10indicate that the power to the LAB-X I js ON andthe poldrityof the bargraph.) The 4 high bits,birsD4 ro D7, cannotbe usedfbr anyofier puryoseifthe LCD is beingused.The sofrwarcdoesnor releasethese4 bits aufomaticallyafterusingthem to fansfer informationto rhe LCD but you do havethe optionofsaving the valueof PORTDbeforeusingrheLCD. and thenrestoringlhis valueaftertheLCD hasbeenwrittento. The complication, ofcourse, beingthattherewill be a shortglitch whenrheLCD is writtento andtheuseyou make of PORTD has to toleratethis discontinuity. PORTE,which hasonly lfuee extemallines,is dedicatedto conlrolling the information transferto the LCD. Theselinescanbe usedfor otherpuryosesifthe LCD is nor being used.PORTEis madedigilal whencontrolling the LCD andcanbe usedfor analoginputs whenits pins arc specifiedas analoginputs.This is donewith theADCONl register asdescribedcarlierandin Chapter9. The LCD providedon the LAB-XI allowsus to displaytwo linesof 20 characrcrs each.Its connections to the microcontroller areshownin Figure5.3. Sincethis is important,let'stakeanotlerlook.In Figure5.3. we seethatthe LCD usesall the lines availableon PORTDandPORTE.All of PORTDis usedasthe port tiie datawill be put on, while PORTE,which has only threelines, is usedro control datatransferto the LCD. We alsoknow from looking at the full schematicsprovided with the LAB Xl that all of PORTD is also connecredto ihe LED bargraph. This doesnot alfect our programmingof the LCD and we will ignore this for now. You will. however,seethe LEDSin the bargraphflicker ON and OFF as programs run, becausewe willbe manipulatingthe dataon ihe lines(D0 to D7).Itis alsopossible to feed the LCD wirh jnsr the 4 high bits ofPORTD. Sce t]ie PBP marual on how to do this. It takessiightly longer to refreshthe LCD when you are using orly 4 bits, and writing to the LCD is one of the most time consuminglasks in most programs. Let's write the ubiquitous"HelloWorld" programior the LCD as our firsr exercise in programminglhe LCD (seeProgram5.4). Oncewe know how to do that,we can basicallyw te whateverwe want,whenwc wan1,to the LCD display.

54

COI{TBOLIIIIGTHE OUTPUTAND FEADIIIIGTHE INPUT

Dntl ENE NE EN EN

i1

EE EE NE EE EE EE NE NE EE NE o

schemalicd agram lrlFiiiiiia:d:3lrl TheLcDdisplay wiring. (An easylo-comprehend r andlhe 2 x 20 dispaynrodule-) showingjustthe llnesbelweenihe micfocontrolle

in the LCDdisplay r'iP-ioCiittu!4]l Displavins andblinking"HELLOWORLD" For the LCD displal rcgistcN oD the LAB XL CLE]AR DEFIIIE DEFINE DEFINE DEFITIE DEFINE DEFTNE DEFINE

clear OSC 4 LCD DREG PORTD IJCD RSREG PORTE I,CD RSBIT O IJCD EREG PORTE ItrCD EBIT 1 LCD RWREG PORTE

I ; ; select , ; enable ; ;

rc asfollows: theDEFINEstatemenls Lhe nenory

register These

registe!

DEFINES

LCD DISPIAY

ipiiiiiiiiiry{i{:l (Continue,tl DEFINE DEFINE DEFINE DEFINE DEFINE

Disprayins andbllnking"HELLOWORLD"in the LCDdisplay

I,CD RVIBIT 2 NCD-BITS A I,CD I,INES 2 I.CD COMMANDI'S 2 0 0 0 ; delay I,CD_DATAUS 50 delay

Set Lhe port directions.

in rnicio in nicro

we are setting

seconds seconds (nust set) all

DooFv6r 'ho!ot aod qtl oI PORTI "s o'-p!i. D o o / d l lines. Th- lo! l bbl- ii D oe set ds path Lo feed the LCD.) a 4 high bit

PAUSE 500 ERISD = %00000000 TRISE = %00000000 A.DCONI=%00000111

I,CDOUT SFE, 1 PAUSE 250 LCDOUIF \HELI,oZ LCDOUT tFE, SCo I,CDOUT \![ORLDZ PAUSE 250 Gctro LooP EIID

of PORTD

Lds o.lr -p--s :.

.\ ep ^e L c

araow ror

LLU srarEup rlnes !o ouEpur s e r a l l P O R T El i n e s ! o o u t p u t oo--o-Drqi ra co-L-o -eg sLor needed for the 16F877A - see above and below this nakes all of poris A and E disitaL. the main loop of the program clear screen, go !o position 1 pause 0.2s seconds ; go to second 1lne,

frrst position

; Pause 0.25 seconds ; all

progxans

must end in

END

Before we can write to the LCD. we have to define how the LCD is connectedto the MCU. Also, since the 16F877A has sone analog capahilities, it w,ill stah p atul rcset in analog rnode,and has to be changedto digital mode (for PORTE onb in ow imme diate case)before we can use its digital properttes. The compiler manual tells us we have to specify the location of thl3LCD and spec ify the confit lines connectedto it so the compilercanaddressthe deviceproperly.Doing so lets us placethe LCD whereverit's converfentfor us when we designour own devices(and the compiler will still be able find it). Thesevariables are to be specified in DEFINE statementsbefore any of the rest of the program is written. (In thjs book, we will alwaysplacethe LCD at the sameaddresslocationsusedby the LAB Xl so we can test all our programsfor our insffumentson the LAB Xl when we need to,) Program5.4 demonstratesthe most elementarycontrol over oulpul to the LCD dis play. Variations of theselines of code, and the addition of a few commandcodes,will be usedto write to the LCD in all our programs. Not all the precedingDEFINE statementsareneededon the LAB-XI, but when you build your own devices,you will needto include them all to make surenothing hasbeen omitted.You neverknow what stateanMCU might startup in, so coverallyourbases.

56

GONTROLLI GTHEOUTPUT AI{DREADIIIG THEII{PUI

ControlIing the Digital andAnalog Settings ADCON1 = Analogto Digital CONtrol register#1. The ADCONI=7.00000111statement,or one lil(e it, is neededior the 16F877A becauseany PIC MCU processorthat hasany analogcapabilities at all comesup in the analogmode on reset and startup.This particular instruction puts all the analogpins on po(s A and E into the digital mode. Since we need or y PORTE and PORTD for con trolling the LCD, noneof PORIA needsto be in digital mode.I am showing E 000001I I becauseall the examplesusedby nicroEngineeringLabs in all their literatureandon theirWeb siteuseandsuggest singthisvalue.Seedatasheet for moredetajledinformation.(Theuseof thisregisteris alsodiscussed in greaterdetailin Chapter9.) If you want 1otum just the three available lines on PORTE to digital, you can useany binary valuefrom 010 to 111inclusive. The conlrol of the A-to D conversion capability is managedby the 4 low bits of ADCONI. For our purposes,bit 0 and bit 3 are not relevant.Seepage 112 oI t}te datasheetfor detailed information on this. Bit 0 is not relevantto the LCD operation(it is a "don't care"bit). Bit I and 2 must be set to 1 to make the two pots (A and E) digital. Bit 3 is not relevantto the LCD operation(it, too,is a "don't care"bit). SoADCON I = '/.000001I 0 or %0000011I would be adeouatefor our work. (Wecould also havedonethis in decimalformat with ADCON 1=6 or with ADCON1=7.)

Writing Binary,Hex, andDecimal Valuesto the LCD The valueof numberswrittento the LCD canbe specifiedwith prefixesthatdetermine if the valuewiil be displayasa binary,a hexadecimal, or a decimalvalue.Seethe PBP manualfor details. BIN specifiesthatthe displaywill be binar). HEX specifiesihat the displaywill be in hexadecimal format. DEC specinesthat lhe display will be in decimal format. In hogram 5.5, the valueof "NMBR" is setto 170arbitrddly (actuallybecauseit alternatesls and0s in binaryfonmt). Any numberbelowor equalto 255could havebeenused. Using BIN8 insteadof BIN displaysall 8 bits. Using Hex2 insteadofHEX displaysboth hex digits. DEC5 can display all fivl. decimal digits becausewe are limited to 16 bits

FEAOII{G A P]OTEIITIOMETERAI{D DISPLAYINGII{E RESIIITS ON THE fEO BANGNAPH

(65,535)andintegermathin PICBASIC.BIN16canbeusedfor 2-bytewordsto display all 16bits.Any numberof digitsup to 16 canbedisplayed. ill!.ijliilii.i:.qoall

writins io the LcD disprayin FULLb;nary hexadecimar,and decimal

CLEAR DEFINE OgC 4 DEFINE IJCD DRIC POR'D DEFINE LCD_DBIT 1I DEFINE I]CD RSREG PORTE DEFINE IJCD_RSBIT O DEFINE I,CD EREC PORTE DEFINE LCD EBIT 1 ADCON1-%00000110 IOIT PoiRTE.2 PAUSE 500

deine LCD connections def,ne LcD connections define LCD connections def,ne LcD connections define LCD connections deflne LCD conneciions rnake PoRTA and PORTE dlgiraL rcD R/\'i 1ow ('rite) We will do no xeadins wait for LCD to starL up

NMAR VAR BYTE

assign variable

TRISD = %00000000 NMBR = %10101010

D7 this

D0 = all outpuls is decimal 170

r.cDou! $FE, $80, BrNS i{MBR,z \,HEX2 NUBR, . ., END

DEC5 N!|BR," .

; display ; end proqran

Readinga Potentiometerand Displaying theResultson theLED B OTESOI{ READII{GTHE POIENIIOiIETERS OI{ TIIE LAB-Xt Eachpotentiometeri s placedacrossground and5 volts alrdthe wiper is readon the A/D line. (Other referencevoltagesand resistances can be specifiedand used-see the datasheet.) The potentiometer valuehasto be high enoughso as not to act as a short betweenthe power and ground. 5K ohms as a minimal value is okay. (Extremely high values make for ajittery reading.) When we read a potentiometer the MCU divides the voltage acrossthe potentiometer into 256 stepsbeiween0 and255 andgivesus the numberthatrepresents theposition ofthe wiperacrosstheconnectedvoltage.Neitherthevoltagenor theresistance of thepotentiometer i s relevanl(thoughitcanbe if we know theminimumandmaximum voltageacrossthe pot). What we aregettingis the relative position of the wiper expressed asan 8-bitnumber.(ThePIC alsohasa 10-bitresolutioncapability seethedatasheet andPICBASICmanual.) The overall resistanceof eachof the threepotentiometersis placedacross5 volts, and lhe threePORTAlines readthe position oithe three pers.The potentiometersar€ read ass-bit valuesusingan s'bitA to D converterThis givesa full-scalereadingof from

COI{TNOLLING THE OUTPUTAND REAOITIG THE INPUT

0 to 255for ail dueepotentiometen,no matterwhatthe actualtotal rcsistarcevalueof edlh potentiometer.If you want to readthe resistancein ohms,you must divide the readingby 255 andmulriplyby thelotal resistance olthe potentiometer(Again,thepotentiometer value must be high enoughso the potentiometerdoesnot act as a shon bctweenglound andthe MCU power comeclion. 5K lo 10K ohmsis a good seleclionfor most purposcs.) Next, we will rcadjust oneof the potentioneten (theonenearestthe edgeof theboard) to an accuracyof 8 bits anddisplaytheresultson the rightmosteightLEDSof the LED bargraph.This potentiometer is connectedto pin 2 ofthe PIC (alsoidentifiedas RAo andaspin PORTA.0).We will displaytheresultof thevalueread(0 to 255)on thebargraphby loading the readinginlo PORTD.Since PORTDis connectedto the eight LEDS,this will automaticallygive us a binary rcpresentationoi the data.ln the next step, we will display the inlormation on the LCD dispiay as alphanumericdata(which js, of course.rnucheasierto read). Exp.ndi4 theprcgramto not only disptayb the baryraphbut alsoput theinformationon theLCD display,we havea prcblemin thatthe PORTDlinesaresharcdby rlrebargmphand fie LCD display-Whenwe run theprogram,we will noticeilat dEre is a backgmundnoisy blinking of the LEDSin the bargraphasthe l,CD is uritten to, b t atur that is donethe bargraphdisplaysthedatalrom thepotentiometerasexpected.If we hadhardwareandsoftware thatcould suppress thc LEDSwhcnwc werewriting to lheLCD, thisproblemcouldbe eliminaled.Theopention observeddemonslrates du1thechip selectline allowsusto usethelines of PORTDto controlboth the I-ED ba€raphandthe LCD display.Oncewe are donewith writing to the l-CD we canloadthe datainto POR'ID andpausethe pogmm to allow us lo readthedisplay.Noticethatthe pause/delay mustcomeimmediatelyaftersettingPORTDto A2D Valuefor this to work properly.when we do wha!,is importantwhenusingmicrccontrollers.Program5.6 showsus how thisis doneandFigure5.4 showstherclevantcinruiiry.

Disprayinsthe potentiometer wiperpositionon the LCDand the l:lpiiltriiiiilEii LEDbargraph CI,EAR DEFINE OgC 4 DEFINE I.cD DREG PORTD DEFINE I,CD_DBIT 4 DEFINE I,CD_RSREG PORTE DEFINE I.CD RSBTE O DEAINE I.CD EREG PORTE DEFINE I.CD EBIT 1 A.DCONI=?0 0000110 IJOW PORTE.2 PAUSE 5OO

; def,ne LCD connections ; , ; ; ; ; ; ; ;

deflne LcD connections denne LcD connections deine LCD connections deine LcD connections def,ne LcD connections def,ne LcD connections Make PORTA and PORTE digila1 LCD R/W low (set it to write wait for LcD to start up

only)

NUIIB VAR BYTE

IRtsD = %00000000 A2D VAI.UE VAR BYTE IRISA = %11111111 A.DcONl = %00000010

to store ; se!

poRTA analog

resuLt

REAltltlc l POIEI{TIOMEIEBAttD DtSPL,AYlitcTHERESULTS Ot{ tHE LEDBAncBApH

59

al!lf-6,i!i!ni!i6ll Displayingthe potenliometerwiperposltionon lhe LCDandlhe (Conttnued) LEDbargraph

DEFTAIE A.DC BIAS 8 DEFTNE A.DC CIOCR 3 DEFXNE .[.DC-S!!|PLEUS

50

paramerers set nunber of bits in result set cLock source (3=rc) set sampling tine in uS

IJOOP: loop ; sLart lllcl![ 0, A2D VATUE ; read channel 0 to A2D_va1ue SVAIJUE- \, LCDOUT $FE, S80, HEX2 A2D VAITUE, " ", DEC5 A2D VATII'E LCDOUT SFE, $COI BT!I8 A2D VAIUE PORTD=A2D VAIJI'E ; the pause nust cone right afLer serting ; PORTD and befo.e PORTD is used again PAUSE 250 setting PORTD before ; try the LCDOUT Go:rO LOOP ; do iL forever END ; end progran

E-F-'FBi

4

l:lF.ii9!!-,.!!el: The baslccircuitryfor the threepotentiometers" {Theinformarion read fron polenLiometerO rs d,spldyed o'1rl-ebarg.aphn Prcgrarr5.6.)

60

THEINFUI READING THEOUTPUTAND COI{TBOLI.II{G

A SimpleBeep We haveoneotherpieceofhardwarcwe canoulputto on thc LAB-XI andthatis the small piezoelectric speakeron the board. This speakeris connectedto line PORTC 2. The PWM (PulseWidlh Modulation)commdndcan be usedto createa shol1beep ofl thc piezoelectricspeakeron the LAB_XI. The commandspecinesthe PORIC pin to be used,the duly cycleandthc durationolthe beep(100millisecondsin our case) SeeProgram5.7. Generatesa short ione on the piezospeaker(Nolethai linec2 is :l!!!'Eii!l$]|:: 1) HPW[jlChannel CI,EAR DEFIT|IE OSC 4 PW!{ PORTC.2, 127. EI{ID

100

end the progran

Bogram 5.7providesa 0.1 second(100psec)beep.Circuirryis shownin Figure5 5' Pressthe resetbulton to rcpeatthe beep. Check to seewhat happensil you leave the END statementoffa 50 percentduty cyclefor 100cycles Prcgram5.? generales

i:l!i!f'!Ci$5:: rhe basiccircuilryfor generatingtones (ll you on the piezospeakeron the hardwareprovidecl. on line 44 appear receiver, its slgnaLwill usethe infrared circuitryis shown.) Onlyrelevant

A SIiIIPLEBEEP

6i

It dennesthatwe areusinga4 MHz oscillaror PORTC.2specifiesthe pin to be used. 127specifiesa 50 percentduty cycle;the rangeof the variableis from 0 to 255. I 00 specifiesthatthetoneis rolastfor 100of rhe256ON-OFFstepsrhatdefineonecycle. In the PWM command,the fiequencyandlcngth of the signaigeneratedaredependenr on theoscillatorfrcquency.In our case,thisis 4 MHz, andonecycleis about2.5milliseconds long (0.0025secondt. Notethattheline C2 is alsoconnectcdto theoutputfor a possiblephonejackandto an IR LED that can be used to interact with IR receiven. Theserwo connectionsate not populatedon the PC board as received but they can be addedwithout diificulty. Two fypesof signalscanbe annunciaredon rhe speakerasprcgrammedfrom the compiler The PWM commaodcan senda signalof a fixed duty cycle ior a fixed number of cycles, and the HPWM commandcan set up a PWM signal thal nns continuouslt in thebackgmund.Ineilhercase,the signalneedsto be Fovided on thePORTC.2pin becausethat is wherethe speakeris connected.However the normalpWM (nor rhe background IIPWM) conrmandsignal canbe madeto appearat any availablepin. The back ground HPWM signal can be modified "on the fly" in a progl:rm. The HPWM signalscan only be madeavailablear pin PORTC.2(Channelt) and PORTC.I(Channel2).Yes,the pin nurnbersarereversed!In the PIC 16F877A,rlrcre are only two IIPWM channelsand rhesetwo pins are connectedpemanently to these twochannels.(SomePICdevicesprovide morethantwo channels. Seethedatasheets.) Since we have the speakerhardwired to PORTC.2,we can only useHPWM Channel I tbr the tones we generate, As seenin Figure5.5,thesesignalscanalsobe usedto generatetelephone dial tones (DTMF) and inftared (IR) signals when provided wirh rhe appropriarehardware.We will concentrateon creating toneson the piezo speaker The w ing and programrning is the samefor the other devices;they are all wircd in parallel. Just changeihe paramProgran 5.8 is a slightly morecompljcatedprogramanddemonstratesthe useof PWM to controlthe brightnessof oneof the LEDSin the bargraph.

iqtiimff5igt

LEDdimming usinsthepwMcommand

CI.EAR DEFINE OEC 4 ERISD : %U111110 X VIR BYTE I.OOP: FOR x = 0 IO 255 STEP 5 Pt{!r PoRTD.o, X, 3 NEXT X

Gdro tooP END

PORTD. O

CONTFOLLINGTHE OUIFUf AI{D READII{GTHE IIIPUT

in thatwe must UsingtheHPWM (hadwarePWM) connnandis abit morecompucated definesarc defiDecertainparameters belbrewe can uscthc comnrand.The necessary DEFINE CCP1 REG PORTC DEFINE CCP1 BIT 2 DEFINE CCP2 REG PORIIC DEFINE CCP2 BIT 1

; , ; ;

Port to be used by IIPI!'I4 1 Pin to be used by HPVil4 1 Port to be used by HPIiTM2 Pin !o be used by HPidM 2

You alsohaveto definewhich timefrhe signalwill useso othertimerscanbc usedfor other purposeswhile the signalis being generated.If a timer is no1spccjiicd,the syslemdclaultsto Timerl. the 16 bit rimer The commandis HPt'lM Channel,

Dutl,cycle,

DEFINE.OSC 4 gPm,t 1, 127, 1500

Flequency

' qe

a, o

6 oJ

MTNPOS IHEN RTTURN

right

CEMTER: POS = 1540-127 RETURN

move servo POS = POS

+ A2D VAIJI'E

END

At this stage,we me startingto getan ideaabouthow onemight takea simpleprob_ lem and make it amenableto a more sophisficatedsolution by adding simple ha(lware and software fea$res to it. We have gone from a simple but rigid control of the posi_ tionofa servoto a muchmoreflexibleanduser-ftiendly approach. Addingfeature;like theseto our insfumentsand controllerswjll make them more inruitive,useful,and

Readin the In uts

Now that we are beginning to leam how to conFol tbe output. we needto learn how to read the inputs and manipulatethe outputs basedon what ihe input is. In orher worals. $ e r r c g o i n g r o l e a m h o $ t o c reei n . tefdcll\e.andrhU.mlr)be;oreu.efulprogfar instruments, andcontrollers.

!=lD_M FnsI COLU|N,FtRsrROwpusHBUrroN(swll

A D TUR oI{ ait LEDol{Ly wHtLErHE BUTToN(swti ts DOWN

The simplestinputis to readjustonepushbuttonanalthe simplestoutputis to tunljust oneLED ON. We will do just rhatbur we will adda tiule complication.The LED is to be programmedto be ON only while the blrtton is held down. We will usebutton I atoD left) on the keyboardand rheLED connectedro PORTD.0.This emutaresthe operarion ofan ordinarymomentaryconractswitchjn anyreal world application.

READII{GTHE KEYBOARD On the LAB-XI, all of PORTBis dedicared to the inrerfacewith rhekevboard.Lines B0lo BJ rre connecledlo thero$i. andLheline\ 84 ro B7 areconnecred ro rhecolumns of fhekeyboard.Whenthe keyboardis not beingused,the linesmay be usedfor other

5A

CO 'NOLLII{O THE OUTPU' AI{O BEADINGTHE IIIPUT

purposes,but keep in mind the intemal pull-up capability and the inline load limiting resistorson the lower 4 bits/lines(80 to B3). Thesecan,of cou$e, easilybe madeto remain outside our circuitry, so none of this is a problem for us. In other words, the keyboard is connectedto PORTB such that the columns ol the keyboard matrix are connectedto the high nibble of a po and the rows ate connected to the low nibble.The whing schemalicis shownin Figure5.7. To rcad a keyboard like this, the low nibble of PORTB is set to be outputs and the high nibbleis setto be inputs. on the PIC 16F8??A,PORTB hasa specialproperty that allows its lines to be pulled high (very weakly)with internalresislorsby settingOPTION-REG.7= 0. This property of the PORT can alTectall the high bits (B5 to B7) but only thosebits that are actually programmedto be inputs with TRISB will be affected. Next,thefour (thelow bits,83 to B0) aremadelow oneline at a time,while thehigh bits are polled to seeif any of them hasbeenpulled low If any of the switchesis down, oneof thelineswill be pulledlow. Becausewe know which low bit wasselectedwhen tlrc high bit becamelow, we can determinewhich key has be€n pressed.For our purposes,al this stagewe areinterested only in swl, theupperleft switch,sowe cansimplify the circuify to whal is shown in Figure 5.8 for one roq and then v/hat js shown in Figure5.9 forjust onekey. In thesediagrams,we canseethatif we makePORTB.olowandPORTB.4hasbeen pulledhigh, PORIB.4 will becomelow only if SWl is held down.No polling is nec essaryat this stage.Once the conditions are set up, all we have to do is cfeate a loop that tums the PORTD.o LED ON if the switch SWI is down and OFF for all other conditions.The codefor this is listedin Program5.13. readsswl andturnsLEDon PoRTD.0 Beadinga swltch (Program ffiwf{6kt!{ ONwhileit is down) CI.E]AR DEFINE OgC 4 tRIsB = %11110000 PoRfB - %11111110

Set only B0 nade ]ow.

OPEION-REC. 7 = 0

lhe pu11 ups on PORTB bi! 7 of lhe oPTIoN REG sets the puLl ups

IRI€D = %11111110 PORID.0=0 IIIAINI,oOP t IF POR!!B.a=1 ELSE PORTD.0=!, ENDIF GOIO I'AINLOOP AND

TEEN

set only initialize

P O R T D . ot o a n o u t p u t . lhis LED to oFF

check for 6ast colrlm being if i! is 1ow turn D0 oFF if

no! turn

it

oN

1ow

",ll

3 l

.,|

; {

;tl

; {

:tl

.,]] =tl

5tl

.,il

d

.ri

51

-.|

.5 tJ

d )

..lt ;'l

"Jt ".fl 5 t dl)

.,ll .Jt ".fl d )

=11

= l

irl

;

ok: Hodi .o;E

!>i

eseE

q-uE EX/

' " \

=;x

.!) ii ccgo

rY>

6>=

tE=

5EAP

diFs

:= =

{

diod

H

fiti

\

ui>4 COtUldN= (NCD BUASER) -4 ; caLculale ROw=riICD (BI'FFER &$0F) ; calculale * 4) +COIIJ!4N ; calculate SWIICE=( (ROw-l) LCDOUf SFE,

SCo? \ROw=,,

\ g$t=/, DEc swrTcn, \ \ RETURN

coLm row swiLch nunlcer the second line ; print DEC ROW, \ COL-Z, DEC COLUMN,

END

andDisplaylts ReadOnePotentiometer 8-Bit Valueon LCD in Binary,Hex, and DecimalNotation,alsoImpressthe A detailed discussionofA to-D conversionsis coveredin tlte chapter,which is devoted to the construction ol a digital thermometerinsirument based on this capability. As mentionedbefore,thepotentiometersarereadby dividing the voltageadossa potentiometer into 256 pats and seeingwhich of the 256 divisions match the position of the

READOIIE POTEI{TIOMETEF AI{D DISPIAY|TS A.B|T VALUEOII LCD

75

wiper.This givesa readingbetween0 and255 (in s-bir resolution).It rloesnot tell us any_ thing abont the rcsistanceof the potentiometet only the relatjve position of the wiper will rcad/usethe pof closestto the edgeofrhe board.This pot js connectedIo line ,We PORTA.o,which is pin2 of the MCU. Dconve$ionsarecontrolledby theADCON0 andADCONI rcgjsters,andthe _ -A-to 16F877Ahas!o be in analogmode for the relativepins fbr A_to D co;versionsto be possible. Settingthe birsin ADCON0. (Seepage l of the datasheet.) Bits ? and6 controlthe clock/oscillator to be used.Serthesebothto 1. Bits 5 to 3 selectwhich chamejsare to be usedin the conversions;setto 000 for PORTA.O. Bit 2 clearedwhenthe conversionis completed.Setit to I to starrthe conversion. Bit I tgnorcdtn A,/Dconver\'onr.Sel ir ro 0 Bit 0 controlsA-toD conversions. Setit to I to enableA-ro-D conversions. Whentheconversion is completed, theresultwill beplacedin ADRESHandADRESL. The^formatof how this is done dependson how the result is set up with rcgister ADCONl. ADCONI needsbit 7 to be set to 0 to make the 8_bjtrcsult appefi in ADRXSH and bit 2 needsto be setto I to selectpotentiometer 0 andsettheproperreferencevoltages. Seepage I 12 of the datasheet. So we setADCONo ro 7.1100000 t ro set p for readingPORTA.0. And we setADCON1 ro q,00000010. Theprcgramsegmentb reada valueis shownin program5.16.

iit|iinliii{$m; in all formats)

DEFINE OSC 4 IJOOP! ADCONo.2 = 1 NOT DONE: PAI'SE 5

Polentiometerreadings(Disptaying the vaiueof lhe potentiometer

; marker

if

not

done

IF ADCO!IIo.2 = 1 IIIEN ArcE_DoNE; wai! for 1ow on bir 2 of AICoNO, conv A2D r|Al,UE = ADRESE ; rcve hish bybe of resul! ro A2D_Va1ue LCDOIIT SFE, 1 ; cleai screen LCDOIIT \VAlJttE: ., DEC t2D-VALtrE,. \. ; display the decinal vatue PAUSE 100 0-1 second ; vail GOTO IOOP

76

CO IROLL|I{GlllE OUtPUt A D nEADll{GTHElllPUT

lhevalueoi thepotenliometer readings(Displaying $nilm$ffiF.Ki# Potenliometer in allformats) {Contnued) 'the.onrl

?G poctun I ouldlook like,he lorlouin8:

DEFINE LCD_DRIG PORID 4 DEFINE LCD-DB!t DEFTNE LCD_RSRTG POREE O DEFINE LCD_RSBIT DEFINE IJCD_EREG PORTE 1 DEFINE I,CD_EBIT A2D 1/Aj-UE 1IAR BY'JE

; deine LcD regislers

r cieate A2D Value !o store resutt SEt PORTA SE! PORTD wet PoRTA lo aLl input wet PORTD to all output conngare and tuln on a/D Modute set PoRTA malos and LEFT justify wait 0.5 second for LcD startup

A.DcoNo. %11000001 ADcoNl = %00000010 PAUSE500

' r ; ; , ;

[ooP: AI)CONo.2= t

t start

IRISA . %11111111 TRISD = %00000000

and bils

conversion

NqF-DOIIE: IA ADCONo.2 = 1 THEN NCri! DONE A2D \rALI'E = t.cDOUt gFE, t|cDOUt[ .DEC LDOUT $FE,

AzD VrrUE, z

; wait for 1ow on bit 2 of aDcoNo, -or \ -rsi on finisl es lo A2D Value A.DRESI| ; move hiqh byte of lesult 1 ; cLear screen \, z \ 3 values VA'!UEDEC A2D_vIlttE, ; Display \rzBIN=zr 'gEX=", BIN8 HEx2 A2D-VALIIE,' 9C0,

PORTDlIrD_vArrttE PAUSE 100 GOIIO I,oOP END

; ; ; ;

dispLays vatue in wair 0.1 second do it forever end Progra

baigraph

to setup theconversionsIn Program5.16,we usedthe namedrcgiste themselves power of the compiler and its prognm next we will use the In the in the section, pots much more convenientlyby using lhe related commandsto read the three ADCIN command.

ReadAll ThreePotentiometersand DisplayTheirValueson theLCD Five of the six pinson PORIA canbe usedasanaloginputs.In our case,phs 0, 1, and 3 are connectedto the tkee potentiometers.(Pin A4 cannotbe used.)

Ifwe wantto rcadall threepots,we haveto activatetheirthreelines andcrcatevari_ ablesto stotethe threeresuhsobrained.The modificationsto progran 5.16areshown rn rlogrami.I / l:lfrii.!ai|ii.i!!!!ar Displaypotentiometersettinss(Reading anddisptaying aI rhree polenliomeiers vatuesin decimattormat) CI]E]AR DEFINE OSC 4 DEFINE LCD DREC PORTD DEFINE IJCD DBIT 4 DEFINE ITCD_RSREG PORTE DEFINE LCD RSBIT O DEFTDIE IJCD.EREG PORTE DEFINE LCD_EBIT 1 rro$r PoRtE.2 PAUSE 500

; define

LCD connections

DEFINE A.DC-BTTS 8 DEFINE T.DC CIJOCT(3 DEFXNE ADC_SA!'FLSUS 50

LCD R/\|7 Line low {td) wait .5 second for LCD srartup rne next.J defines axe needed for the ADCIN comand se! nunber of bits in result set inLernal clock source (i=rc) set sanplinq riine in us

T R X S A= % 1 1 1 1 1 1 1 1 TRISD = %00000000 AncoNl = %00000110 A2D Valueo vAR BytE A2D_Va1u61 VAR BYTE A2D VA1UE2 VAR BYTE

ser PORTA to alt inpur set all PoRTDliaes to outpurs PORTA and PORTE Lo digital create A2D-vaLue to slore r.esult create A2D Value to srore resulr create A2D value to store resutt

LCDOUT SFE, 1

clear

IdAINI,oOP r

the display

; maan progran toop ; cnec]. porentioneter vaLues ADCTN 0, i2D VALttEo ; read chaanel 0 ro A2D-VatueO ADCIN 1. A2D_VAIJUEI ; read channet 1 to AzD vatuel aDctl{ 3, A2D VArruE2 ; read channel 2 to A2D va1ue2 rrcDour $FE, 980. DEC A2D-VAIrUEo," \,DEC A2D,VAIJnE1,' \ ,DEC A2D_VArtrttE2, z \ PAUSE 10 GOFO UATNLOOF do it all forever EIID

1 2 3

'F

COXTNOLLIXG ?TE OUTPUTAI{D BEAbINGIHE IIIPUT

Adding the Kind of Flexibility That DefinesComputerInterfacesand Demonstratesthe Ability to Make Real-TimeAdjustments Sophisticated Program5.18 is riruilar to Pn gram 5.16 that r)as derdloPed€drlie. but showsanother apFoach. Use the threepolentiometersto conlrol one R-/Cselvo. Control the relative location of the centerposition with POTo Controllimit positionof the endpositionswith POT1. Confol the rate of movementwith POT2. (Threepotenliomelers conirolling one seruo/Potentiometers ffiffimalx*fK program) lofthls servoiconnecltheservoto JumperJT CI,EAR DEFINE OSC 4 DEFIIIE I,CD DREG PORTD DEFINE I,CD DBIT 4 DEFINE IJCD RSRAG PORTE DEFINE I,CD_RSATT O DEFINE LCD_EREG PORTE DEFINE t,CD EBIT 1 LOW POREE.2 8 DEFINE ADC_BIES DEFINE ADC_CI,OCK 3 50 DEFINE ADC,SA!IPI,Et'S TRIgt = %11111111 TRISD = %00000000 .ADcONl = %00000111 VTJI BYTE A2D VII-I'E \rAR BYAE AzD VII.UEI A2D_VA',UE2 VlR BYTE POS VAR I'IORD CENTERPOS VAR VICRD IIAXPOS VAR }IORD IIINPOS VAR IIORD POSSTEP VAR BYEE PAUSE 500

deine

LCD connections

LCD R/w line low (r,i) set number of bits in resulL set clock source (3=rc) set sanplinq line in us seL PORTA to a1t input se! all PORTD Lines to outputs PoRTA and PoRTE to digital create A2D-Va1ue to store resulL creare A2D vatuel to store result cieate A2D Value2 to store result se.vo posl.1ons

t servofpotenriomerers rrrree pore,ltiomere.s corro,t,nsore llll]l: -5..1lhe servoro Jurrpe. servo:coine.l J7 lo.ft s p.ogra.r|ttContinued)

SERVO1 VAt PORTC.I ADCIN O, A2D VII-UE OPTION_REG E S01111111 IJOW SERVO1 GOSUB CENTER ITCDOUE $FE, 1 poRTB = 0 TRISB = %11111110 !'AINIOOP: IF PORIB.4 IF PORIB.5 IF PORTB.6

alias servo pin read channel 0 ro A2D Value enable PORTB pullups servo outpur low cLears screen only PORTB lines 1ow ro read buttons enable f,rst button rod nain prosrar loop check aay but. pressed ro

= 0 TBEN GOS('B = 0 TEEN GOSITB CEN!ER = 0 THEN COSUB RIGIIT

a.Dcrar 0, a2D_vAIrnE ADCIN ADCIN

1. 3,

A2D_VAIUEI A2D_VAI,I'E2

MAXPOS=1500 + A2D-VALUE1*3 MINPOS =1500 - A2D-v!!UEt*3 CENTERPOS=1500+3*(A2D_vaJ)vE_I27

read channel 0 to a2D_Value read channeL 1to A2D_vatue 1 read channet 2 to AZD Vatue 2

POSSIEP =A2D VATUE2/1O +1 SERVO1 = 1 start servo putse PAUSEUS POS SERVOI = 0 end serwo pulse I]CDOUT $FEI $ 8 0 , \ P O S = - , D E C p O S IJCDOUE $FE, $CO, DEC A2D VATUE,/ \,DEC s , DEC_ A2D VAIrtEl,/ POSSTEP, a \ PAUSE 10 ; servo update rate about 60 Hz GOTO !'AINI]OOP do ir LEFT: IF RETURN

; all forever ; move servo Lefr POS < llA)(POS THEN pOS = pOS + POSSTEp .

RIGHT: IF RETURN

POS > UTAIPOS TIIEN

POS

vo.^

= POS

--_.o -

!:q. POSSTE'

CENTER3 POS = 150 0+3* (A2D VA',IIE_127) REEUXN END

, end proqran

Exercises Carlion:Thinkingrequiredl An.q e^ ro lh.4eprobjem\dn Mt prc,ida1.thereareno unrque.oturion\. rlr(e mcunpInnrumenl.rnd ronlroller,i, rcdll)allabourinput. andouFul, and whatyoudo wirh them,a comprehensive serof exelc;*.,fr" t-, .p*in""fiy J, i"p"i" ancloutputsareprorided.

AO

TI{EINPUT IHE OUTPUIAI{DBEADING COTTNOLLIIIG

LED EXERCISES:COIITROLLINGTHE LIGHT ElulTTll{G DIODES(LEDsl We will leam aboutcontolling the outputfrom a PIC by writing a seriesof increasingly complicaled programsthat will conlrcl the ten-segmentLED bargraphprovided we areconrolling the LEDS'but fie controlstrate on the LAB-Xl.In theseexercises, giesdevelopedwill applyto anykind of"ON OFF'deviceswe haveconnectedto the LAB-X1 or to any otherdevicewe design. I . Light the eight LEDS on the righl one al a time till they are a lit' andthen turn then OFF oneat a time. Time delaybetwe€nactionsis to be one-tenthof a second(exactly) 2, Modify theprecedingprogramsothedelaytime is conlrolledby lhetop mostpotentiometeron lhe LAB-XI. The time is to vary from 10 millisecondsto 200 millisecondsinclusive,no less,no more. 3. Write a programthat wi ll vary the glow or the rjghtmostLED from fully OFF to lully ON oncea second.Programthe sccondLED to go dark dndbdghi exacdy I 80 degrees out of phasewith the first LED so that asone LED is gelting brighter, the other LED is gettingdiDmer andvice versa. 4, Write a programthat flashesihe lbur leftmost LEDSON andOFF every 0.25 seconds and cycies the four LEDS on the right lhrough a bright/dim cycle every two seconds 5, Write a programthatflashesthefirstLED tentimesa second,flashesthesecondone rhelhird I fD $hene\erborhLLDs r-reon ar lhe nlnerime.a.econd.rnd n,1.1'e. sametime. Display how many times the third LED hasblinked on the LCD display. but haslo havea commondividerso thethirdLED will (Timingcanbe approximate give the beatliequency.)

LIOUIDCHII|STALDISPLAYEXERCISES!COI{TROLLING IHE LIOUIDCRYSTALDISPLAY(LGDI of tbe memorylocationsusedby the LCD haveaheadybeer fixed' as The addresses has the instruotionset we use to write to the LCD The descriptionof the Hitachj tID4,l780U(LCD-II) controllerinstmctionsel asweil as ils electroniccharacteristics are provided in the dala file for the display.Here, wc will list only the codesthat apply to our immediateuseof the devioe. Two typesof commandscan be sentto the display:the contlol codesandthe selof charactersaresuppofied' actualchamc€rsto be displayed.Both uppelcaseandlowerca-se codesallow you to congraphic The contro] chaJacters as are a number of specialaltd trol thedisplayandsetthepositionofthe cursor.andsoon.Eachcontrolcodemustbe preceded by decimal254orHer $FE.(Theoonfol]er alsosupportsthe displayofa set of Japanesecharactersthat are not oI intetest to us ) Commandcodeslor thefollowing aclionsarcprovidedalongwith others.Go to thc datasheel for the conlrollerto find out what all ihesecommandcodesale Clear the LCD Retumhome

Go to beginring of line 1 Go to beginningofline 2 Go to a specificpositionon line I Go to a specific position on line 2 Show the cursor Hide the cursor Use an underline cu$or Tum on cursor blink Move cursor.ightoneposjtion Move cursorleft oneposition Therc are still other commandsto discoverin the datasheet,There are memory loca tions within the LCD, aswell asinvisible locationsbeyondthe endof the visjble 2b char_ actels.You should know how to find all this information. It is also possibleto designyour own font for usewith this parficular display. All the information neededto do so can be found in the Hitachi t{D447g0U manuayd;sheet. l. Wdte a program to put the 26letters of the alphabetand the ten numerals in the 40 spacesthat are available on the display. put four spacesbetweenthe numbers and the alphabetto filt in the four remaining spaces.Once all the charactershave been entered,scroll the 40 charactersback andforth endlesslythough the two lines of the display. 2. Write a progmm to bubble the 26 capital letters of the alphabettbrcugh the numbers 0 to 9 on line two of the LCD. (This means:First put the numbersoi line two. .,A,i then talcesthe piace of the ',0,' and all the numbersmove over. Then the ,A,, takes lheplaceofthr"l"andthe 0 movesto po\ilionL Aierward.the-A..rcphcei lhe r anoso on Uttrt getspa\llheq Follouing rhr(.lhe..8..sran\irswa) acrosc trhe numbersand so on.) Loop forcver. 3. Write a prognm to write the numbers0 to 9 upside down on line l. Wait 1 second and then llip ihe numbersrighr side up. Loop. 4. Createa programto write ..HELLO WORLD,, to the alisplayandthenchange it to low ercaseone tener at a time with 100 millisecondsbetweenletters.Wait I second and go back to uppercaseone chamcterat a time with negativeletters (all dorson the dis_ play are revened to show a da* backgroundwith white lettersin lowercase). Loop.

MISCELLAI{EOUSEXERCISES Theseexercisesate designedto challengeyour programming ability. Again, you will need accessto ihe datasheetlbr the LC Display.

A2

THEI{PUIANDREADING COI{TROLI.II{G THEOUTPUT

I . Editor: Write a programthal dispiaysa random 12 numberson line I of &e LCD and displays a cursor that can be moved back and fo h acrossthe 20 spaceswith potentiometer 0. The entire range of thc potentiometermust be used to move acrossthe Allow thekeypadto insertnumbers0 to 9 into the posilionthe cursoris 20 spaces. on. Assigna deleleswitchand an insertspaceswitchon the keyboard.A comprehensivenumber(plusdecimalandspace)editoris required 2. Mirror Write a program that puts a random setof letters and numberson line 1 and iheo puts their mirror imageson line 2. The mirror is betweer linc I and lirc 2. You have to learn how to createthe upside-downrumbers from the Hitachi datasheetior thedisplay,andalsolearnhow lo readwhal is in the displayfrom thedisplayROM. on eachline. The displayROM is capableof stodng40 characlers 3. FortyCharacters: on all 40 characters you and forlh to see program to scroll back to allow Design a line one fol each poientiometers for scrolling, both lines one line at a time. Use two 4. Four lines:Wnte a programto displayfour linesof randomdataon the LCD andto scrollup anddown andsideto side1oseeall fourlines in theirentiretyYou haveIo lt whenyou storewhat is lost from the screenbeforeit is lost so you canre_create 5. Bargraphs:Crcatea three-bdrgraphdisplay,with eachbar 3 pixels high' that extends acrossboth lines of the LCD. The lengthsof the bargraphsare detemined by the se! tings of the threepotentiometers,which changeasthe potentiomete$aremanipulated. By no\ you shouldbe gettingpretty good at using lhe 16F877Aand are nearly irady to finishthe introduction.Only a little moreandwe will be readyforjust that!

TIMERS AND COUNTERS

General If you have no knowledge about timers, you should read this chaptercarefully before taking on the chaptersthat follow. Those chaptersprovide a much morc advanceddiscussionof the devicesbasedon their usage,as opposedto the introductory approach prcvided here. However, there is somerepetition, so as to allow eachpart of this book to standindependendy. Most userswill frnd that using time$ andcountersj s the hardestpart of leaming how to usePIC microcontrolle$. With this in mind, we will Foceed in a step-by-stepmanner andbuild up the programsin piecesthat are easierto digest. Once you get comfoftable with their setupprocedures,you will find that timels andcountersarc not so intimidating. We will cover timers andcountersseparately-Countersare essentiallytimers that get their clock input ftom an outside so rce. Therc are two countersin the 16F877A, and they areassociatedwith Timero andTimerl . Timet cannotbe usedasa counterbecause it hasno way to rcad an extemal signal into this timer. No|€ Theclockfre.quercyutilizd by the timersis o e'foul'th ofthe os,:illatorfrequencj. This is thefrequencr of the instuction clock. This meansthat the counte^ are allected by everyfounh count of the mdin oscillator. TheIrequenct is rcfeffed to as Fosc/4 in the literaturc . Whenrcspondingto an extemal clock sigwl, the responseis to the actual frequencr ofthe input. Caulion ThePICBASICPRO Compilergenerutescodethat doesnot respondto inter rupts \thile a conpiled instruction is being executed.Therefore,lone PAUSEs(meanins long enoughto los. ar interrupt sig/al, dependiB on how the tirur is set up) cdn l.ad to lostinterruptsif morethanoneinterruptoccws during thepaute. Sinceinterruptsare used neeAr,thisis mostundesirable. for theexpresspurposeoJhandlingcritical response/timing PAUSEcomnandsshouldbe usedwith careunAertheseco ditions.Theprcgrum samples ptorided nen give emmplesoI how theJ can be wrixen to generateshorterpauses.

A4

TIIIIERSAI{DCOUIITERS

Timers andexam Timedlwill be coveredin moredetailasa protollpicaltimer,anddiscussion plesfor the useofTimerl andTirner2will be providcd. is a bit morecomplicatedthanwhatwe The useoftimers internalto microprocessors amountofsetuprequiredbefore thercis a considerable havebeendoingso far because the optionsfor settingup the timersareextenthe limercan be used,rnd alsobecause sivc.We will coverlhe timersone at a time in an intoductory manner,but be warned that there is an entirc man\al (Plcnicro Micl RangeMCU Faniry Rekrence Manual lDS33023l)availableliom MicrochipTechnologyInc-thatcoversnothingbut timers' so our coverageherewill, olnccessity,be rudimentary. how to tum themON andOFF timershasto do with understanding Understanding in ihe andhow to readandsetthe variousbitsandbytesrhatrelatcto them.Essentially, typicaltimer applicatiot,you turn a tiner ON by turningon its enablebit. The timer thencountsa certainnumberofclock cyclesand setsall interruptbit, thus causingan intemrpt. Youlllprogmm respondsto the intenupt by execntinga specifc inkrrupt han' dling routine ard iJ|'et\clearingthe intenupt bit. ]lhe progra"nthen relurns to wherever haveto do with modifyingthe it was whenthe inteffuptoccurred.The pre/postscalars place. pail is findingou! which bit does The hard time it takesfor an inteffuptto take what and where it is located, so readingand understarding the datasheetchaptcron the tiner you areusingis imperative.Thereis no escapingihis horrorl Timersallowthemicrcontmller to cr€aFandrcactto chronologicalcventsTheseinclude: : I I I ! !

Timing events The creationof clockslbr variouspurposes Generatingtimed interrupts Controling PWM generation Wakingthe PIC from its sleepmodeat jntervalsto do work (andbackto sleep) Specialuseoflhe watchdogtimer

The PIC 16F877Ahasthrceintern.rltimers.Thereis alsothewatchdogtimer,which afterthe standardtimers. is discussed It's the t Timero An 8-bit free-runningtimer/counterwith an optioDalprescalar. to use. of the timers simplest ! Timerl A 16 bi! tiner that canbe usedasa timer or asa counter-It is the only I6-bit of thetimers. timerthatcanbe usedasa counter.Itis alsothemostcomplicaled postscalar and cannotbe usedas a r Timer2 An 8-bit timer with a prescalarand Therei. n,JInpullrnefor rhi. lim(r. counrer. Eachtimer hasa timer control registerthat selsthe optionsandpropertiesthat the timer will exhibit.All thetime$ aresimilarandeachof themhasspecialfeaturesthatgivc it for the PIC l6F877Aas specialpropertics.It is imperativeyou referto your datasheet what ihe PIC you experimentwith the timer functions.Onceyou startto understand together in yourmind will start to come areup to wilh lhe timerfunctions.it designers

fllitEFo

Timers can have prescalarsand/or postscalaNassociaredwith rhem that can be used to multiply the timer setting by a limited numberof integer counts.The scalitg ability is not adequateto allow all exacttime intervalsto be createdbut is adequatefor all practical purposes.To the inability to createperfectly timed intenupts, we have to add the uncertainty in the fiequency of the oscillator crystal, which is usually rct exacrly what it is statedto be (andwhich is affectedby the ambienttemperatureasthe circuirry warms up). Thoughfairly accuratetimings canbe achievedwith the hardwareasrec€ived,addi tional software adjustmentsmay have to be added if exrremely accumte results are desired.The softwarecan be designedto make a correctionto the timing every so often to make it more accurate.We will also need an extemal sourc€that is at least as accurate as we want our timer to be, so we can veriry the acclrmcyof the device we create.

TimerO l-€t's write a simple program to seehow Time works. We will usethe LED bargraph to show us what is going on inside the miqocontroller. As always, the bargraphis connectedto the eight lines of PORTD o{ the LAB Xl. First,Iet's write a programthat will light the two LEDSconnectedto D0 andDl alter nately.(SeeProgram6.1.) Having them light altemarelylersyou know thar the program is running, or morc accurately,it lets you know that the segmentof the program that conlainsthispan of thecodeis working.Thesetwo LEDSwill be usedto repr€sent the foreground task in our program. There is no timer processin this program at this srage. There are no interrupts. The programjust blinks the LEDS. Foregroundprogramblinkstwo LEDSalternately(Notimeris being lF!i0E!]!ffiS: usedin thisprogramatthislime) CIEJAR DEFINE OSC { TRISD . t11110000 PORTD.I - 1 IIIIPHA 1IAR WORD MAIAILOOP ! IFPORIFD.1=0XHEN PORTD.I = 1 PORTD.O = O EIJSE PORTD.I = O PORTD.o - 1 EI1IDII' FOR.NTPSA=1TO300 PAUSTOS 100 NEJI(T II,PIIA GOTO MAIIILOOP END

make D0 lo D3 outputs turn off bi! D0 turn on bit D1

the next tines of code turn if lhey are oFF

and OFF if

this uith

the LEDS ON

they

loop replaces a lonq pause comand short pauses thal are essentially r ' 1 1 6 . | ^ . | , ' c ' . | ' ' '

do it all forever all prosrds need to end with

END

A6

flMENSA D COUNTERS

The useof the PAUSEUSloop in the Prognm 6.1 Fovides a latercy of 100microsec onds (worst case)jn the rcsponseto an jnlemrpt and eliminates most of the effect of changingthe OSC irequency if that shouldbecomenecessary.It is better than nsing an empty counter, which would be completely dependentof the frequency of the system oscillator. (There is an assumptionhere that the 100 psec latency is completely tolerable to the task at hand, and it is for this program. It may not be for your real world pro gramthough,so itmay needto be adjusted.) We are tuming one LED OFF and anotherLED ON to Fovide a more positive fe€dback. As long as we are executing the main loop, the LCDS will light alternately and prcvide a dynamic feedbackof the operation of the program in the foreground loop. we select a relatively fast ON OFF cycle so we will better be able to see minor delays and glitches that may appearin the operation of the program as we proceed. Run this Fogram to get familiar with the operation of the two LEDS. Adjusl the counter(the300 value)to suityour taste. Next, we want 1oadd the codethat will interrupt this progmm periodically ard make a third LED go ON and then OFF using an approximately one-secondcycle. This will seNe asthe inlerrupt'ddven task we are interestedin learning how to create.This is the IMPORTANT task in this pa icular exercise. Herc is what must be addedto the plogmm to get the intenupt-dnvenLED operational. EnableTime0 and its inte[upts with appropriateregister/bit settings. Add the ON INTERRUPT commandto tell the prc$am where to go when an interSet up the inlerrupt routine to do what needsto be done. The inteffupt routirc countsto 6 1 and turns the LED ON if it is OFF and OFF if it is ON. Clear the illterrupt flag that was set by Time . Sendthe program back to where it was intenupted with the RESUME command.

WHY ARE WE USII{G 6I ? Theprescalar is setto 64 Oits0 to 2 aresetat 101h theOPTIONREG). Thecounterinterupts every256counts, 256x 64= 16384 Clockis at4,000000Hz Fosc/4is 1,000,000 = 61.0532.Its 1000000/ 16,384 notexactly61,butit is closeenough tbr ourpurThelinesofcodenowlooklikethosein kogram6.2.

TtMEnO

67

,:a*{!ii!niFiigi usinsIMERo (ProglambtinksrwoLEDS[D1andDo]ailernalety and blinksa thirdLED[D2]lor onesecondON andonesecondOFFas conlrotted by the interruplsignal) j

D E F I I | EO S C 4

'ed-

'6noj\

j usidga4MHzoscillaror

OPTION F-EG=%10000101 ; page 48 of daLasheeL pu ups o orJ! B ; bit 5=0 selects tiner node i biL 2=L j ; biL 1=0 ] seLs Tinero prescala. ro 64 ; bit 0=1 ] IiCTCON=%10100000

A L P S AV A R v I O R D BETA VAR BYTE

; : ; ; ; j ;

bit 7=1 Enables alL umasked intefuupts b r 'Erao.aqTim- 0 ov-rfow - -e--.p brt 2 flag wiLl be ser on inieriupt and has lo be cLeared in Lhe inlerrupt rouLine. rt is set clear ar srar! nis v". i"ble co- . : n r l - D a u s dr S o o p this variable counLs the 61 intefupt

IRISD - %11110100 ; sets lhe 3 output pins in the D porr P O R T D= % 0 0 0 0 0 0 0 0 ; sets all pins row in the D porr aEtA=0 ON IIITERR[IPT Go:rO INTROUIIAIE ; this Line needs to be early in ; lhe progran, in dy case, before the routine is ca11edMATN']OOP: IFPORID.I=0THEN PORID.I = 1 POR!D.o = 0

EI,SE PORTD.I - 0 PORID.o - 1 ENDIF lOR tl,PEA = 1 TO 300 : PAUSEUS100 NEXI AI,PIIA GCIIIOIIAII\ILOOP DIS.ASITE

ne:r

_ooo

b ilkp D0 dno D. o

the foreqround

l6

as described

_or s peL.F _s -t wlcn

DISABLE//ENABLE nus! interrupt routine

n'ra

snort

bIKt

-d

ar or6ly

before

/i .q -

Lateocv

the

s

ee

fl ERsat{Dcout{TEns

and blinksiwo LEDS[D1andD0]allernalelv UsinsTlMERo(Program a:!!4ff!!il{l.g* as conlrolled bythe one s€cond OFF blinksa thrrdLED[D2]foronesecondON and inlerruplsignal)(Contlnued) IMIROUTINE:

; bhis infornation ; odLv'

ls used bv Lhe conpiler

BETA=BETA+1 IF BETA< 51 TIlriN ENDMITERRUPT ; one second has noL vet passed = BEEA 0 ; loop lurns D3 on and off everv tF PoRTD.3 = I IHEN ; inlerrupi PORTD.3= 0 ; 61 tines through the inter:rupt routine. EISE ; ThaL is about one second per fulL cvcle = PORED.3 1 ENDIF t ETIDTNIIERRUPT tN!coN.2 = 0 ; clears the inlerrupt flaq, REAU!@ ; -esua h6 ma:- o oo dn ENAS!,E ; DISABLE ANd ENABLENUSTbTACKCT routine ; the interrup! END ; end prograrn Make your predictionsandthen... Try changing the 3 low bits in OPTION-REG to seehow they affect tbe operntion of the interruPt. In Program6.2, Timer0 is runningfree and providing an interruptevery time its 8 bil counterovedows from FF to 00. The prescalaris setto 64 so we get the interrupt "lntRoutlne" routine, where after 64 of thesecycles.When this happens,we jump to the we make surethat 61 intetrupts have taken place,and if they have, we changethc sfate of an LED andretum to the placewherethe interupl took place.(It happensthat it takes approximately 61 inteffupts to equal one secondin this routine with a processorrun ning at 4 MHz. This could be relined by trial ard error after the initial calculation ) "IntRoutine" routine, but the Note that the interrupt is disabled while we are in the ireerunningcounteris still runningtowad its nextoverflowmeaningthatwhateverwe if we arenot goingto missthe nextinteralohasto get donein lessthan 1/61seconds rupt, unlesswe make someother arrangementsto count all the interupts (with an inlernal subroutine or someother scheme).It can becomequite complicated if a lot needs to be done, so we will not worry about it here Before going any further,let's take a closerlook at the OPTION-REG and the INTCON (intenupt control) register.Theseare 8_bitregisterswitb the 8 bits ofeach registerassignedas follows: OPTION-REG the option register: Bit 7 RBPU.Nol ofinterestto us at thistime.(This bit enablesthepo( B pull ups-) Bit 6 INTEDG. Not of interest to us at this time. (The intefiupt edge select bil detemineswhich edgethe interupt will be selectedon, rising [1] or falling [0]). Eitheroneworksfor us.

TIMERO

A9

Bit 5 T0CS,Timer0clock selectbit. Selectswhich clockwjll be used. I = Transition on TOCKI pin. 0 = Internalinstructioncycleclock (CLKOUT). We will usethis, thc oscillator-Seebit 4 description Bit 4 TOSE,sourceedge selectbit. Detemines when the counter will increment. I = Increment on high-tolow transitior of TOCKI pin. 0 = lncrementon low-to-hightransitionof TOCKI pin. piII. Decideswhat thepresca]arappliestoBir 3 PSA,prescalarassignment I = SelectwatchdoCtimer (WDT) 0 = SelectTimero.We'rill be usingthis. Bits 2, 1, and 0 define the prescalarvalue for the timer. As mentioned edrlier, fie prescalarcan be associated with Timeroor with the watchdogtimer (WDT) but not both. Note that the scaliflg for the wDT is half the va]ue for Timero for the samethree

Bit vaiue

TMR0 rate

WDT late

000

ltz

lrl

001

l:4

1:2

010

1:8

l:4

011

1:16

1:8

100

t:32

l:16

l0l

l:64

l:32

ll0

1:128

1:64

111

11256

1:128

Wewill usethis.

Caulion A rery specifc sequencenust hefollowe.l (which doesnot apply here) whetl changins the prescalar assignmentfron Tiner, to the WDT to make sure an unintendedresetdoesnot takeplace.This is describedin detdil in the PICmictu Mid-Ranqe MCU Foni\, RefercnceManual (DS33023) As per thepreceding,in our specificexample,OPTION REG is setto 7.10000101. Refer to the datasheetfor more specific information. ll{TCOl{ the intemrpt control registervalues are as follows: BitT=l

Enablesglobalintenupts.

Bit 6=l

inleruplr. Lnable'all pcnphcrdl

Bit5=I

Enablesan interruptto be setonBit2 belowwhenTime overflows.

Bit 4 = I

Enablesan inte[upt if RBOchanges.

90

flMEnS Al{t COU TERS

Bit 3 =1

Enablesan interupt if any of the PORTBpins areprogrammedas inputs and changestate.

Bit 2

Is the Intempt flag for Time .

Bit I

Is the Intenupt flag for all intemal intertupts.

Bit 0

Is the Intefiupt flag for pins 87 to B4 if they changestate.

Note that Bit 2 is set clear when we start and will be sel to I when the iirst interupt takesplace.It has to be re-clearedwithin the interrupt service routine thercafter.(This so.) is usuallyat the endofthe routine,but not necessarily

A TIMERo CLOCKTFROMA PROGRAIIIBY IUICHOENGINEERIiIG LABS lot{ THETRWEB SrrE) The following program,written by microEngineering Labs and prcvided by them as a part of the information on their Web site, demonstratesthe use of intemrpts to createa reasonablyaccurateclock lbat usesthe LCD display to show the time in hou$, minutes,

LCD CLOCK PROGNA USINGOII INIERRUPT This program usesTMRo and prescalar.Watchdogtimer should be set to OFF at programtime,andNap andSleepshouldnot be used. Buttonsmay be usedto sethous andminutes. In Program6.3,the CLEAR andOSC commandsare not used,but we will ahvays usethem in our programs. Labsprogram(Hou|s,seconds, Timerousageper mlcroEngineering iili!!ii.!i!t!i!l:l andminulesdigitalclock) DEFINE DEFINE DEFINE DEFINE DEFINE DEFINE

I,CD_DRIG PORTD I,CD_DBIT 4 I,CD_RSREG PORTE IJCD_RSBI' O IJCD_EREG POREE LCD_EBIT 1

IIOUR VAR BYTE DEOUR VAR BYTE IIINUTE VlR BYTE SECOND VAR BYTE ETCRS VAR BYTE UPDAIE 1IAR BYTE I VAR BYTE A.DcoNl = %00000111 LOII PORTE.2 PAOSE 100

denne LCD connections

define hour wariable hour variable define display denne ninute variable denne second variable deine pieces of seconds variable define variable to indicare update of LcD de bounce loop wariabte parls of PORTA and E nade digrital LCD R/w Lov = write wait for LCD to startup

l|MERo

9t

(Hours, seconds, TimercusagepermicroEngineerlng Labsprogram l8fagiiifl${:: (Corlinued) ock) andminules digiialc ; ser inirial

rine

ro 00:00:00

MINUTE = 0 SECOND = 0 TICKS = 0

; force flrst ; , ; rN:rcoN = %10100000 ; ON INTERRI'PT GOTO TTCKINT ; !4AIIILOOP: ; ; TRISB = %11110000 ; PoRTB=%00000000 ; : oPTroaI_RtG - %01010101

IF IF IF IF

PORTB.T PORTB.6 PORTB.s PORTB.4

CHKttP:

IF

= =

0 0 0 0

ttlEN EBEN EEEN EIIEN

DECIIIN INCIIIN DECHR INCHR

last

2 bulcons

set ninute

f,lsl

2 butbons

set

hour

OPDATE = 1 4HEN

disptay tine as hh: m: ss change hour 0 to 12

DHOLR = SOUR IF {EouR // 12) = 0 lsBN DHOttR-DEOUR+12 ENDIF IF

display i c..,-

-.--... r6.184 nilliseconds and enable set fl'IR0 connguration PORTB pullups enable TMRo inlefupLs ; nain progrran toop in this case, i! only updaLes ihe LcD with the it enable aLl buttons PoRTBlines Lor !o read buttons 'he'n dll orrio_ P Ass6d o " rine I

HOI'R < 12 EIIEN check for !-14 0r PM \ lU{?' \.2, DEC2 seconil, LCDOIII DEC2 DHOUR. ":", DEC2 IIINUIE, EIJSE DEC2 SECOND, r,cDotrt DEcz (DHouR - 12), \:'?, DEC2 MrNUrE, s:,, \ PM/ ENDIF

ENDIF GCTO MAINI,OOP INCMIIiI: MIIiIUTE = MINUTE IF MINU:rE >- 60 tllEN MINUTE - 0 ENDIF GOTO DEBOT'NCE

+ 1 ;

; lncremen!

hours

92

IIMEIS AIID COUNIERS

Labsprogram(Hours,seconds, Tlme0 usageper microEngineering digilaiclock)(Coniinued) andminutes IIOttR = SOUR + 1 INCER. IF EOttR >= 24 IPHEN HOttR = 0 ENDIF GOTO DEBOUNCE = MIIID:TE DECMIN: MIIIuIE tF IIINuEIE >= 60 tgElil MIIiID:rE = 59 ENDIF GC|IIO DEBOUIiICE XOUR - EOUR DECER: >= 24 !EEN IIOUR IA ItOt R = 23

-

decremen!

ninutes

decrement

hours

1

1

ENDIF

; de bounce and delay for 250 ns DEBOUNCETFORI=1!!O25 PAUSE 10

, 10 ns aL a tine

so no intettupls

NEXT I UPDATE = I GOTO CEKI'P

DIEABNE

, interrupt

routine

; disable

interruPEs

to hddle

each

durinq

TICXINAT EICRS = TICKS + 1 IF TICKS < 51 THEN IIE:IIIT

; ol1e second eLapsed - update tine IICKS = 0 SECOIiID=SECOND+1 tF sECOND >= 60 IHEN SECOND = 0 UINUIE=r[INurE+1 tF UINITTE >= 50 ESEN = 0 UINUIE ltottR=EOITR+1 IF HOttR >= 24 THEN llot R = 0 ENDIF EIIDIF ENDIF UPDAIE = 1 - 0 INICON.z EIEXII: RESI'ME END

, se! Lo update LcD ; reset timer inierrupt

flael

llilEEt:

IHE SECONDTIIER

93

In the precedingclock, the keyboard buttons are usedas follows Swl andSw5 incrementthe hours. SW2 and SW6 decrementthe houls. SW3 and SW? incrementthe minutes. SW4 and SW8 decrementthe minutes. The secondscannotbe affectedotherthanwith the rcsetswitch.

Timerl: The SecondTimer Tbe secondtimer, Timerl is the 16-bit timer/counter.This is the most powerful timer in andusebut is alsothe the MCU. As such,it is the hardestof the timersto understand most flexjble of the threetimers. It consistsof two 8-bit registersand eachregistercan be rcad and wdtten to. The lmer can be sedeither as a timer or as a counter depend ing on how rhe Timerl clock selecrbir (TMR ICS), which is bit 1 in the Timerl coftol register(IlCOl0, is set. In Timerl, we can control the value that the timer startsits count with, and thus changethe frequencyof the inte[upts. Here we are looking to se€lhe effect of changing the value preload into Timerl on the frequency of the interrrpts as The higher the value ofthe prereflectedin a very rudimentarypseudo-stopwatch. get load, the soonerthe counterwill to $FF and the fasterthe inteffuptswillcome. We will display the value of the prescalarloadedinto the timer on t}le LCD so we canseethecorelation betweenthe valuesandthe aclualoperationof the interrupts, As tlle intefupts get closer and closer together,the time left to do the main task getssmallerand smallerand you can seethis in the speedat which the stopwatch In thefollowing program: SWl tums the stopwatchon. SW2 stopsthe stopwatch. SW3 resetsthe stopwatch. POm, the filst potentiometer,is readandthenwritten into TMR1H. (TMRIL is ignor€d in our case,but you may want to useit in a morc crjtical application.) The (esults of the expedment are shown in the LCD display. Let\ creep up oII the solution. We will develop the program segmentsand discuss them as we go, putting the segmentstogetherlater lbr a program we can run, as shown in Program6.4.

94

ftiltERsa D coul{TERs

of onvaLue ihatdepends timeroperation ittLi-qatilafris!:llTimerlusage(Budimentary POT-1) ; 6rst fet us seL up lhe ; CLtlaR ; DEFITIE OgC 4 DEFINE IJCD DREG FORTD ; ; DEFIIIE LCD DBIT 4 DEFME l,CD RSRBG PORTE ; 0 DEFTNE IcD,RsBIt ; DEFINE LCD-EREG PORTE ; DEFINE LCD,EBI! I ; poRTE.2 = O ; PAuSE 5OO ;

LCD dispLav parmeLers. cleai nenory set osc speed lcd is on PORT'D plolocoL use 4-bit we will selecL reerister relrister seLect bit regisLer enable Re€risLer enable bil node set for vtile 5 seconds wait

; NeaL Let us deFne the variables we uiLl be usins cleate adval to store result

AD1/Ai V,IR BYTE TICKS VAR WORD TENTES VAR B'TE

sEcs vax woRD MINS

VAR BYEE

; set the variable ; but a formaLity

to specifrc vaLues, not necessarv in thls for cLariLY

progrm

TICKS = 0 TEMUIS = 0 SECS = 0 MINS = 0

; ; set the re€rislers Lhat will conlroL the fork c a l l out each bit g r i t t v w e w i l l o f i t s o n i l L y i s t h e T h i s ; control register. ; I N T C O Ni s L h e l n t e r l u p ! =%11000000 INICON rhis has io be seL Enable bi!, ? : G I E: GlobaL Interrupt b i t ; to worK; for any interrupt 1 = Enables all un nasked interrupts ; 0 = Disables all inteIrupLs ; Enable bit 5 : P EIE: Peripheral htertupt b i t ; 1 = Enables alL un-masked peripheraL intefupLs r 0 = Disables alL peripheraL inLert\rpts ; Enabte brt ; bit 5: TOIE: TMRo overflow Interupt = T!IR1 interrupt the I Enables r o = Disables the TlG1 inlerrupt ; Enable llt , bib 4: INTE: RBO/INT ExternaL Interrupt intelrupr = exLernal RBO/INT Enables lhe I ; inteirupt = e x L e r n a l t h e R B O / I N T D i s a b l e s 0 ; (Coklikue.t)

llMERl: tHE SECOIID TllilER

95

thaldepends onvalueol limeroperailon ini{fii{!{1qj.411 Timerlusase(Rudimenlary (Continued) POT-1) ; ; ; ; ; ; ; ; i ; ; , ; ; ;

b1!

bi!

bir

bit

3: RBIE: RB Port Chanqe lnLerrupt EnabLe bi! t = Enables the RB port change intetrupl o = Disables the RB port change intefupt Flaq blt 2: T01F: TMRoOweiflov hterrupt has overflowed (must be cleaxed in 1- = TMRo resisler softvare) did not overflow 0 = TMRo resrster FLag lrit 1: INTF: RB0/rNT External Interlupt (nusl be occurred interrupb 1 = The RBO/IN1' externaf cleated in sofLware) oc u 0 Tn- PBo \l 6aL4 'ol ,nr err-pt d_d 'o FLag bit O: RBIF: RB Port Change Interrupt L = At leas! one of the !B7:RB4 pins chansed state (nus! be cleared in software) 0

Non-

o

."e

DB

:oBl

p:n

na

e

chd' qod

s

q

P

; TlcoN is Lhe tiner 1 contro} reqister. =%00000001 TlcoN '0' ; biL 7 6: Uninplenenred: Read as ; bit 5 4: TlcKpsl : TlcKPso : Tinerl hput Clock Prescale selec! bits 11 = 1:8 Prescale value ; 10 = 1.4 Prescale vafue ; 01 = 1.2 Prescale vafue ; 00 = 1.1 PrescaLe vaLue ; Enable control bi! TloscEN: Tinerl oscillator ; bit 3: is enabled I = oscillator ; inwerter is shut off (rhe osciltaLor 0 = oscillator ; pooex drain) is Lurned off Lo elininare ; Sl4chronization T1S1NC: Tinerl External CLock hput ; bit 2: conlro1 bit ; TIIR1CS = 1 ; j clock inpu! external L = Do noL synchronize extelna1 clock input 0 = Synchronize ; TMR1CS = 0 ; clock This bit is ignored. Tinerl uses the inlernal w h e n T M R 1 C S= 0 . ; T M R . L c s :T i n e r l c l o c k s o u r c e s e l e c r b i t ; bit 1: ! = External clock from pin RCQ/T1OSO/TICKI(on the r risiner edge) ; cLock (Fosc/4) 0 = Internal ; TMRION. Tinerl On bit ; biL 0: ; ; The oplion

0 = Stops Tinerl regisLer lContirueA

E6

TIMEES AIID COUNIERS

Timerl usage (Budimentarytimer operationthat dependson vaLueof iit&iitiilii$all POTI) (Continued) OPTION REG = %00000000

; Set Bit 7 to 0 and enable PORTBpullups ; A11 other bits are for Tiner 0 and ; noL applicable

PrEl=%00000001 ; See datasheet, enables interrupt. ADCOTiIO= %11000001 , co!6gure and turn on A/D ]lodule t b r L l 6 : A D C S I :L D C S o : ; A / D C o n v e r s i o n C r o c k S e l e c L b i t s 00 = Fosc/2 ; 01 = FOSC/8 ; 10 = FOSC/32 ; L! = FRc (clock derived fton an Rc oscillation) t ; b i t 5 3 : C H S 2 : C H S 0 :A n a l o g C h a n n e l S e l e c t b i t s 000 = chamel 0, (FAO/ANO) ; 001 = chamel 1, (FA1/AN1) ; 010 = channeL 2, (RA2/}N2) ; 011 = channel l, (RA3/}N3) ; , 100 = channel 4, (RA5/aN4) 1 0 1 = c h a n n e l 5 , { R E I ] / A N 5 )( 1 ) ; . 1 1 0 = c h a n n e l 6 , { R E 1 / A N 6 )( 1 ) 1 1 1 = c h a n n e l 7 , ( R E 2 / A N 7 )( 1 ) ; ; b i t 2 r G O I D O N E :a / D C o n w e r s i o n S t a l u s b r t If ADoN = 1 See bit 0 ; | = a/D conversion in progress (serting this bit slarts i the A/D conwersion) ; (This bit is not in prosress 0 = A/D conversion ; A/D hardvare then the cleared by autonatically , ersion is conplete) Read as ; 0; ; bit 1: uninplenented: ; bit 0: !-DON: A/D On bit 1 = A/D converLer nrodule is operating ; 0 = A/D conwerter nodule is shutoff and consumes no ; operaLrng current ; ; The A to D conrrof Reqister for Port A is ADcoNl A D C O N I = % 0 0 0 0 0 0 1 0 ; s e t p a r t o f P O R T Aa n a l o g , The refewan! table is on paqe !L2 af the datasheet ;

- h - - . ! .

r o i

; and allow ; on the

the woltage

third

Line

; reference

.lown in

; Nex! 1et us set up IRISA = %11111111 ; TRISB = %11110000 , PoRtB.o = 0 ;

- s , , i h o

the set set seL

the

e u - d ' d l o s

q p d o

i - i . s

belween vdd and Vss. We have

tabte

port pin directions P O R T At o a l L i n p u t u p P O R T Bf o r k e y b o a r d r e a d s so we can read ror 1 only for now (Coktihuet)

flfiEnl: THESECODTlllER

9Z

onvalue01 thaldepends limeroperalion i:BFli.!;ll$qipi Timerlusage(Rudimentarv POr-1)\Cantinued) ; tells

oN INITERRu?EGoto lErcKIM!

Lhe progran

MAtt{looP: aDcoNO.2 = 1

; conwersion

converslon

; now and takes place dutinq Loop for !haL' ; shor! we would allor to decide ; then check lhe bultons IF POR!TB.4 = O TSEN STARICLOCK ; IF PORTB.s = O TEEN STOPCI,oCK ; IF PORTB.5 = O BEEN CI,EA'RCI'OCK;

i :li,:"'1"1*

; We are now teady E ADRESII Al|tl!

Gctto MAINI OOP

{3zrDEC2 SECS,

; disabte , inLerupt + I

tF ttrcRs < 5 TEEN fErE)2o EIIEN EPWM 2. ADVAIJO, LCDOUT $FE, $80,

32000 DEC4X,

r,cDouT $FE. $c0.

"DEC jIwAl-l, ,DEC ADVAIJO, Z

"

.

EI,SE

t cDorx! sFE, $c0,

.P!t!l

roo r,ow \rDEc aDvlrlo, z

\

EIIDIF GOTO LOOP ENI)

Play with the valuesof the two potentiometersto seewhat happens.Be carcful about overllowing the counterpast 255. Unexpectedresults can appear. The Timer0 counter is affected by rhe OPTION REGISTER bits as follows: OPIION_REG.6 = 1

; Inrerrupr on rising edge

OPTION_REG.s = 0

; Extemal clock

OPTION-REG4= 1

; Increment on falling edge not used

=O OPTION_REG,3

; Assign prcscalarto Time

OPTION-REG.2= I

; I These3 bits set rhe prescalar

OPTIONREG.I= 1

; I You can experiment wirh changingthese3

=1 OPTION_REG.O

; I bits to seewhat happens.

Put theseand other valuesin the program and run the program. Se€what happens.

USINGIIMERI AS A COUIITER The operationofTimeil as a counteris similar to the operationofTimer0, but because Timerl is a | 6-bit timer,muchlongercountscanbe handled,andcounrscomingin at faster ratescan be counted.h also meansthat a lot more can be done in the Timerloop and Blinkerloop routines if the program is designedto do so. However, the setup for Timerl is more complicated becauseof the more numercusoDrionsavailable. Thediffercnce. belween theuseof rher$o timershaveto do s rth lheserupot lhe controlling rcgisters.Timerl is controlled by/usessix registen ascompa(edto threefor Timero. They are: INTCON

Intenupt control rcgister

PIR1

Peripheral intefiupt register I

{0s

rl

PIEI

Peripherai inte upt enableregister 1

TVRIL

Lo$ bl|f, oflhe limerrcgisrel

TMR1H

High byte ofthe timer register

TICON

Timerl inteffuptcontrol

Again, the frequency of tbe oscillator is djvided by 4 before being f-edto the counter whenyou usethe intemalclock (Fosc/4). reads: Page52 of the datasheet by settingbit TMR 1CS.In thismode,thetimerincrements Countermodeis selecteal on everyrising edgeof clook input on pin RCI/IIOSI/CCP2, when bit T1OSCENis ser,or on pin RCO/T]oso/TlcKl, whenbit TloscBN is clearcd So three of the piDs on the l6F877A can be used as inputs to the Timerl counter moduie. They are: Pin PORTA.4 which is the extemal clock input. Pin 6 on the PIC Pin PORTC.0 selectedby settingTIOSCEN=1 Pin PORTC.I selectedby settingTIOSCEN=o Timcrl is enabledby settingT1CON.0=I. lt stopswhen this bit is tumed off or disabled. by T lCON.I Theextemalclockis selected TheclockthatTimerl will usels selected this extemal clock must be on PORTB4 1. The input ior setting this to by TICON, provideslhe following control register, bits in the Timerl In summary,8 functions: Bi{4-N#3-re€d.es-a-e $46---+eg$ed*iid Bit 5

Inputprescalar

Bil4

Input Fescalar

Bii 3

Timerl oscillatorenable

Bit 2

Timerl extemal clock synchronizalion

Bit 1

Timerl clock select

Bit0

Timerl enable

If the interrupls are not going to be used,the othel rcgisters can be ignored SetTlCON=E00110001. The settingofthese bits is descdbedin detail on page51 ofthe datasheet.Let's took at Program6.?, which reflects the precedinginformation.

cout{tEns t09 ; Frrst 1et us deflne all the deines that {e si11 need, ; Here all lhe def,nes are included as an exanple bu! ; nor all are needed when using the LAB X1.

l:?t!itii!i!;li:l

Timerlas counter(Tmerlcounts signats froma motorencoder)

CIJE]AR DEFINE

; 4 MEz clock

OSC 4

DEFIIIE LCD DREG PORTD DEFIAIE LCD RSREG PORTE DEFIAIE I]CD-RSBI![ O

DEFINE LCD-EREG PORIE DEFIAIE DEFIIIE DEFINE DEFINE DEFINE

LCD.EBIII 1 LCD-RttlRlc POREE LCD_RWBT!! 2 I,CD.BITS 8 LCD-LINES 2

da.d /E9'

r-g:s '6'6' A

; enabLe reqisrer ;

read/vrite

reqrsrer

read/vrite tidth of lines in DEFME IJCD_COMMANDUS 2000 deray in DEFTNE IJCD_DATAUS50 delay in : l-a-,r ./o lin6e d6tu6\1 r p_n ; that will ; at

control

rs allached

; ; ; , ;

bit data display micro seconds micro seconds s9o,.9

Lhe speed of the noLor.

ooe

The encoder thaL we

to the noto.

DEFINE CCP1 REG PoRTC

; define the HPI,il,tsetLings

DEFIIiIE CCPI BIT

; pin

;

Ih-

r-l

2

r'6

C1 r6od

10

potentiometers on the board. Only lhe first potentioneier is being used in the progran but Lhe orhers are defined so rha! you can In6 por 6r o --ar- Si e ,o- oo, Y you vafues you can change in real tine, define the A2D waLues DEFINE ADC BITS I ; set nun'ber of bits in xesulL D E F T N EA D C C I T O C R3 ; set internaL clock source {3=rc) mFINE ADC SAMPITEUS 50 ; set sanpling tine in uS ; Next we set ADCON1 to bring the MCU back inro diqitaL mode. ; Srnce lhis PIC has analoq capability, ir cones up in ; analog node after a rese! or on starrup. ; set the Analog lo Digiral cont.ol .eqister A!COI{1=%00000111 ; needed for the LCD operation ; re create the variables rhat we wiLL need. l[MRl VAR ]IORD for rhe riner ; ser rhe variabte .A.DVAIJo VAR BYTE ; creare adwaL !o store resulL A.DvALl VAR BYTE ; creaLe adwaL to store resulr a.DvA!2 VAR BYTE , creare adwaL to store resulr

IIO

TII'EESANDCOUI{TEFS

-

:iiFiliiliieii a,? (Continued) X VAR }IORD Y VAR WORD PAUSE 500 T,CDOIIT gFE,

Timerl as counter(Timerlcounlsslgnalslrcm a molorencode4

1

ERIsc = %11110001 ccPlcoN = %ooooo101 rlcotir = %OOooOO1l

PORTC.3-0 PORTC- 2-1

; Next fe go inLo

for experinenlation tariable for experinentarlon variable for LcD to slrart up Display and cursor hone

; ; , ;

spare spare pause cLear

; ; ; ; ; ;

I/O set uP ihe register P o R T c -0 i s q l o i n g t o b e t h e I n p u L caplure ewerv rising edge on no prescale/osc offlsvnc source/TMRl on external sLart the notor, usinq a notor encoder

; enabLe Lhe n'olor ; set the rotation the bodv of Lhe prograi.

direction fhe

though tne are using ; Lhree potenlioneters the ; set Pover ; and thus the speed of the notor.

A.DCIN 1, ADCIN 3,

rhe frrst

one Lo

0 to aDvAL!

read chamel

a.DclN 0, a.DvAl,o

onlv

watn

toop stails

ADI/AI,I A.DVA'"2

; If Lhe duty cycLe of the notor is tess Lhan 20 out of 255 lhe ; notor wiLl noL cone on on ihe condition ; so we make an allowance for ihat and displav IF

ADVAI,O>zo IEIIEN HP9!M2. AD\rBlo, 32000

r,cDour sFE, 9C0, *Pl'l![ = El,SE t cDour ENDIF

\, DEC ADVAIJ0, '?

.,DEC $FE, Sco, 'Pl{li TOO LOW

Then we read the case the

In

our

it

can be isnored

ro add this tMRlE = 0 TMR1L = 0 T1CON.o = 1 PAUSE 1OO

cwo tiner counts

ltDVArJo, /

to

see hov nanv coun's

to

shou up in

regislers

were too

Lo{

j.f vou hawe a faster

but

infornatiod ; ; , ;

\

coun!

the

input,

high vou

to the readout clear Tinerl high 8_bits clear Tinerl low 8-bits slarL 16 bit tiner caplure 100 ns of Input clock

Frequencv

cout{TERs ttl

sisnats froma motor€ncoder) il:P,lliiiAfi:gtaalTlmerlas counter(Timerlcounts (Continued) TlCON.o = 0 ; stop 16-bit Tiner TDIRI. BytEo = T!'R1L ; read Lor 8 biLs TURI.EyTEI - TMRUr ; read High 8 bits $lRl = tDlRl - 11 Correction ; caplrre IF IMRX = 65525 ![EEN ![OSIG![AL ; see PICBASTC pRO manuat LCDOu T SFE, PAUSE XO GO/rO LOOP

S80,

DECs A ! t R 1 , z C O I I N T S '

a.ad-rcr

for

o:splal

NOSIGNAI,3

rcDour $FE, $80, \No

TGTiIAI "

;

GC|IO LOOP EIiID

PRESCALARSAND POSTSCALARS Prescalarsand postscalarscan be confusing for the beginner.Here is a simple A prescalaris applied to the systemclock and affects the timer by slowing down the systemclock asit appliesto the timer. Normally, the timer is fed by a fourth of the basic clock frequency,which is calledFosc/4.Ina systcmrunninga 4 MHz clock,rhetimer seesa clock runningat I MHz. If the prescalaris setfor I :8, the clock will be slowed down by anothereight times,and the timer will seea clock at t25 KHz. Referto the diagram on the bottom half of page 52 (for Timerl) in the darasheetto seehow this appliesto Timerl. Apostscalaris appliedafterthe timercountexceedsits ma\imum value,generating an overllowcondition.The postscalarseningdetemineshow manyover|ows will go by betbrcan interupt is triggered.If the postscalar is setfor 1:16,rhetjmer will overllow 16timesbeforeanjntenuptflagis set.Theupperdiagramon page55 (fbr Timer2) of the datasheetshows this in its diagrammaticform and is worth studying. All othet thingsbeinqequdl,bothpre andpastscala$arc usedtohcreasetheti e bet,reenintertupts. Whenstartingout,just leavethe scalarsat l:l valuesand nothingwill be afiected. We will nol needto usethem lbr any ofrhe experiments we will be doing.Onceyou get more sophisticatedin the useoftimers, you canplay with rhe values andleam more abouthow to usethem.The primaiy useis in creatingaccuratetiming intervals for communicationsand so on, becauseno extemalroutiDesare necessary whenthis is done with scalars.w}len doing it this way,everyrhingbecomesinternal ro the pIC andis thereiore not affectedby extemal disturbances. Additional infomation on timer modules is available in he Plcmicro Mi.l-Ra pe MCU Fanib Re|brence Ma"dl (DS33023).

tl2

ttllEBs al{DcoulltEBs

Exercisesfor Timers l. Write a Fogram to genemtea l-minute time/clock with a 0 1 seconddisplay Check its accuracywith the time site on the Intemet Make adjustmentsso it is accurateto within 1 secondper how' and then I second per day.Can this be done?wlty? Which timer works best?which timer is the easiest to usefor such a task? 2. Wnte the precedingprcgmm for eachof the other two timers.

Exercisesfor Counters I. Desigl analmakea tachometerfor smallmodel airqaft engines Have a ftnge of liom 5 rcv per secondto 50 POOrer per minute displayedon the LCD in real-time 2, Design and build a thermometerbasedon the changesin frequency exhibjted by a 555 timer circuit behg controlled by a themistor. Calibmte the thermometerwith a lookup table. If you arc not familiar with the useof lookup tables,you shouldundertake the researchnecessaryto understandhow to use them. They are very useful devicesat the level we arc working.

clocKs, MEMORYAND SOCKETS

Sockets U3. U4. andU5: For Serial One-WireMemoryDevices Most PIC microconfol]ers comewith a certainaDount of ofl-chip memory This memory is enoughfor most applicationsoeated for thesetiny processo$,but therearetimeswhen more memory is neededto get thejob done.The LAB-XI hasnve empty 8-pin sockets. Three of these(the three on the left) are designedro allow us to experimentwith three types of single-wire memory ICs. The ICs doll'r needjust one wire for fuli control, but the data doesgo back and fofth on one wire. Nole Each metnry socketacceptsonly one Ope of mennry (levice,and onlf one of the lcs is allowed to be in place at any one time becausethe lines are sharettbetween the sockets,so haying more than one deviceplugged in can create conficts. Depending on the type of memory you want to experiment with, one of the ihree schematics in Figue 7.1 is applicable. The interfaces that have be€n developed for the three types of one-wire memory give you the choicesyou rced for flexibility in boarddesignand layout, but it also means that a single intedace and protocol wonl work for everything. The intefaces vary jn speed,number of signal lines, and in other impoftant details. Since the memoriesarc all orc-wjre sedal devices,their memory content can vary irom 128 bytes to 4 kilobytes or more and still maintain the s-pin interface. The salient chamcteristicsof the three types of memory are as follows: r I2C SEEPROM I2C SEEPROMSare serial, etectrically erasableand programmable, read-only memories.They are best suited for applications needing a modest amountof inexpensivenonvolatilememorywherea lot of VO lines arenot availablefor memorytransfers.Requiresfour lines for control,

tl4

CLOCKS.ilEfORY. AllD SOCXETS

4.7K

I

I

ca

0.1

I2CSEEPROM

I

/cs SO

fc3 c5

SPISEEPBOM

CS CLK D1 DO

I

c8

0.1

t OBG

Microwire SEEPROM

c -f0 c8 0.1 I

L

can I,iflgni!$.El!l&one-wirememorysockets.(Thelhreetvpesol memoryyou im;ni;ilh on the LAB-X1andtheirwiringlayoulsionlyone lC may be in place

SOCKE1UE-|2C SEEFROIII

tl5

Microwire Miuowire is a NationalSemiconductor standard andis speciallysuited to usewith their microcontrollers. Thoughoften calleda three-wireinterface,it is actuallya five-wireinterfacewith four signallinesanda ground. SPI SPI (serial peripheralinterface)oiginated at Molorola. 11is much like Miffowire, thoughthe signalnames,polarities,andotherdetailsvary.Like Microwire, SPI is oilen rel-e ed to as a three-wire interface, though a read/write intedace actually requirestwo datalines,a clock, a chip select,and a commonground,making

Othermanufactur€rsDrovideDroductsto meetthe standardslhat havebe€nestablished.

Which EEPROMTypeShouldYou Use? I2C is the bestEEPROMtypeto useifyou havejusttwo signallines1ospare,or ifyo havea cabledinterface(I2C alsohasthe strongestdrivers)Ifyou want a clockratefasterthan400 kHz, useMicrowireor SPI. For moreon usingserialEEPROMS,rcfcr 10the manulaclure$'pageson the Wcb, especially the following sites: I National Semiconduclor wwwnational.conr,/design/ (Containsmanyapplicationnoteson Microwire) r Motorola Semiconductor www.mcu.motsps.com/mc.html (Onsitemicrocontroller reterences containSPI documentation,) JanAxelson'sarticlein Circ&t Cclldr is a good sourceof detailediDfomation on these devices.The article can be fbund at wwwlvrcon/files/seeprom.pdf. The PICBASICPRO Compilerprovidesthe insnuctionsnecessary to accessthese In dll the programsI have listed in this chapter I have usedthe programsand documentationverbatimfrom the microEngineeringLabsWeb sitc. I did this fbr two rcasons. One,to not reinventthe wheelsincethe work hasalreadybeendoneby microEngineedng Labs, and two, to exposethe readersto how the programsare structuredby a programmerotherthanmyself.Eachprogrammerhashis or herown styleofdoing things anditis well wofth beingexposedto the work of otherprogrammers.

SocketU3-I2C SEEPROM SocketU3 accommodates l2C memoryonly.Figue7.2andProgram 7.1illustratcthc useof thismemorytype.

'fi6

AllD SOCIGIS CtocKs. MEMORY.

c8 0.1

scL

A2

SDA I2CSEEPBOM

(Wiring requirements.) andcircuitrv l2CSEEPROM.

ffi*t$ eliijffi!!&t$S

Programto readtromandwriteto l2c SEEPROMS

Lalrs progrd ;This mictoEngrineerinqt l a t e s ! version. U s e l h e ;Web site. CLE]AR €o coN 0 N2{00 coN 4 DPITI CPIN BO 1IAR 81 1IAR 82 VAR

be found

on rheir

oulput define serial seE serial node def,ne variables I2c daia pin

VAR PORTA. O VAR PORTA.I EYTE EYITE BYTTE

Pin

variabLe declararion wariable declaration variable declaration to El}e nenory write

FoRB0=0To15 r2cwRltE DPIN, CPX[,

sAo, B0'

IBo]

PAUSE 10

write each location's address to itself each deLay 10 ns after is needed urite

NEXT BO

FOR BO - 0 TO 15 STEP 2 I2CREJtrD DPIN, CPIN, $AO, BO, SEROUI'! SO, N2400,

I*BL, "

IEl,

^'1/ 82'"

827

read 2 tocations prlnt CRT

2 Localions

print

a line

NEXT AO

S E R O U TS O , N 2 4 0 0 , [ 1 3 , 1 0 ] GOEO LOOP EMD

feed

rn !o

SOCKET U4-SPI SEEPROM

117

c8 0.1

(Wi ngandcircuilry sPl SEEPRoM. requi€"

ire&Ei$ ments,)

SocketU4-SPI SEEPROM SocketU4 is wiredto useSPImemoryonly.Figure7.3 andProgram7.2 illusfate the useof this memorytype. il€Wiiiiii$ilg.i

Prosramto readfrom andwrireto sPl SEEPRoMS

rhis nicroEngineerinq Labs prosran can be found on their web sile. Use lhe lalest version, PICBASIC PRO progr:an to lead and write to SPI SEEPROMS Write lo lhe f,rst 16 locations of an external serial EEPRoM oe.d F-sc 6 locat iors bdck and send Lo -cD lepeaLedly N o ! e . F o r S E E P R O Mw Si t h w o r d s i z e d a d d r e s s e s DEFTNE IOA.DER USED 1 ; allows use of the boot , ; ; ; : ;

; this will not affect ; normal progrm operation. DEFINE

I'D

DEFINE DEFINE DEFINE DEFINE DEFTNE INCIJUDE

I,CD_DBIT 4 IJCD_RSRES PORTE IND_RSBIT O IND_EREG PORTE I,CD_EBIT 1 \MODEDEFS - BASZ

DREG PORTD

t ta

clocl(s, lilEMoFY.aNDsocKEts

{lflwffielg$

Prosramto readfromand writeto SPISEEPRoMS loontinued)

CS vaR POREA.5 SCR VtR PORTC.3 st vAR PoRfc.4 so vAR PoRTc.5 ADDR VAR IIORD BO 1IAR BYTE fRIAA.5 = 0 .a.DCoN1-%00000111

; ; ; ; ; ; ; ;

chip select Pin clock Pin data in Pin dala out Pin AddIESS dAlA set cs !o ouLput sel all of PoRTA and PoRTE

I,ow PORIE.z P A U S E1 O O FOR ADDR = O TO 15 BO = IDDR + 100 GOEog EE9IRME PAUSE 10

; ; ; ; ; ;

LCD R/1,{ line 1ow (W) wait for LCD to slart uP loop 15 tines B0 is data for sEEpRoM to SEEPRoM vrile each delay 10 ns after

lilEltt .ADDR LOOP t

; loop 16 lines FOR ADDR = O IO 15 ; read from SEEPRoM cosuB EEREAD ; displav t cDoutE $FE, I, ila.DDR," t ',jfBo PAUSE 1000 NEKT A.DDR GOIO rnoP EEPRoM Lo read daia fron addr in serial ; subroutine EEPROM CS = O , enable sexial EERETA.D: SEIFTOIXT SI, SCK, TIISBFIRS', T$03, ADDR.BYTEI, ADDR.BYTEO] ; send read cmd and addr SHIFIIN SOr gcR. !!SBPRE, [Eol ; Read daLa ; disabte cs=1 RE{I'RN dala at addr ; subr to write EEPROM ; in serial EEWRITE: : erab_'set a EEPROM Cg=O comnd sgItTOrrT st. scK, lrSBFrBsI, IS061 ; send w:rite sable to execute comnd , disable Cs = 1 ; enable cs=o SHIFfOu ! gt, sCK. !|SBFIRSI!, T$02, ADDR.BYTEI, !.DDR.BYEEO. BOl ; Sends address and dala ; disabte cs-1 RETURN : ; end Program EiND

SocketU5-Microwire Devices SocketU5 is wired to useMicrowjre memory.Figure 7.4 and Program7.3 illustrate the useof this memory type.

soct(Et us-i cRowtRE DEYtcEs I i 9

A

T

u5 A5 c 3

c 4 c5

c

CS l t

1 2

D 11 3 D0 14

l

Slvdd! 7 P E

c8 0.1

6 O R G I ] ] l 5 vss -

Vl".ri,-SeePnOU

(Wilngand sEEPRoM. llFiiiii€:?i*lli l4icrowire

This microEngineeingLabsprogram(Program7.3)-to readand write Microwire SEEPROMdevices{an bc lbund on theirWebsite.Usethe latestversion. i:!(itliatOlli!:t:

Programto readrromand write to MicrowifeSEEPRoMS

S E E P R O I ' I9 3 L C 5 5 A 6r d'.dl .6,-a11sr o o L DDOv Read irst 16 locacions back and send to LCD repeatedLy Doov. wiby.6 .z-d "dd -., \o e: ,o s DEFINE LCD_DREG PORTD DEFIIIE IJCD_DBIT 4 DEFIIIE IJCD_RSREG PORTE DEFIAIE IJCD_RSBIT O DEFIAIE LCD_ERTG PORTE DEFIAIE IJCD_EBIT 1 IIICLUDE \!'ODEDEFS . BAS" CS VTR PORTA.s CLR VAR PORTC.3 DI VAR PORTC.4 DO VAR PORTC.s ADDR VAR BYTE BO VAR BYTE LOW CS LOVT PORTE.2 PAUSE 100 GOSI'B EEWRITEEII FOR A.DDR - 0 tO 15 BO=ADDR+1OO GOSI'B ESI,{RIEE PAUSE 10

def,ne LcD registers

chip select

and bits

pin

chip select inactive set PoRTA and PoRTE to digrrtaL LCD R/lr,i line low (ld) uair for LCD to start up enable SEEPROM writes B0 is write

data for SEEPRoM to SEEPROM (Coktiku..t)

r 20

ct ocKs. MElrollY.allD socKEls

&llmnfriffilg

SEEPRoMS Program lo readfromandwriteto Microwke

(Continued,

NEXT A.DDR rrooP: FOR ADDR = O IO GOSOB EEREA,D

15

LcDorxr SFE. 1, *aDDR,": ',iiBo PlusE 1000

i ; loop i TEAd

16 tines fTOTN SEEPROM

; displav

NEXT A.DDR GOEO LOOP !o tead daLa fron addr in serial ; sl}broutine EERE]ADt ; enable serial CS=1 I%1100\4' ADDRI aEIFtrouT Dt, ct/R, ItEBFIllsI, SEIFETN m, cs=O RETURTI

cIiK, ![sBPOsf,

lB0]

EEPRoM EEPROI,I ; send read cnd ; and address

, read data ; disable

data a! to write ; subroutine EEPROM ; addr in serial EEPROM ; Enable serial ErgrRrtE: CS = 1 SHIRIOT'T DI. CI,K. MSBFIRST, IZ1O1O\{. A.DDR, BOT corEnand, address ; sends wrile ; and data ; disable cs.o RET('RI{ _'oPoM ; subrouline ro aaoblc wrj.ep ro seria. subrouline EEWRIAEEIiI: ; ; enable serial EEPROM CS=1 sErFTOtt! Dr. cr,K, MgBFtRsr, I%10011\5. 0\71 enabLe cnd and ; send wrile drurrny ctocks ; ; disable cs=o AEIFORN END ; end Proqra

SocketU6-Real-Time Clocks Four options are available for using socketU6. This socketis designedto let us experiment with three real-time clocks and with a l2-bit analog_to-digitalconverter' It con nectsto the microcontroller as shown: As shown in Figure 7.5, this is a four wire interface betweonthe MCU and the lC The wiring for this chip is similar to the wiring for the Microwire SEEPROMSand the Microwire memoryICs. Essentially,this looks like a memorychip to the pmc€ssorWhen we write to ihis memory, we are writing to the clock, and when we readfrom this chip' we are reading an ever cha.ngingmemory content lhat gives us infomation that we can interpret as 'lime." So the progam to read and write to this clock looks like a program that interacts with the Microwire fanily of SEEPROMS (SeeProgram7.3 )

SOCKEI U6_REAL.TIMECLOCKS

121

35

ooo12

19

22

REAL.TME CLOCK.OPTION1

-----o

THE7 LTNES MARKED L|KETl{S ARE THE7 LINESTHATGOTOTHE20x 2 DISPLAY IT,ODULE. TH S NoTAToN ISUSEDTI]AOUGHOUTTHE BOOK.

(Tolhe [.lCU,lhisclocklC looksikea set rifElll9li5.:i: CtockimplementedusinglC NJU6355. of memorylocations.)

The sameis truefor the otherchips.SeeFig res7.6 and7.7. TheNJU6355,the DS1202,and the DSI3U ftal ti le docks are the threeintegrated citcuits for use in socket U6. Nole 1 Jumpet JS v,hichis usedfor soldering in the ctystalfor the clock ICs is dlso the connectionthat the anulog signalfor the l2-bit A-to'D co efter goesinto. So,iJ Jo solderin a crystul,fouwill h e to removethe crystaLa d makearra gementsto rcad in the analog siqnal \rhen you wa t to erperiment with the LTCI298 L2-bn A-bD conyerter The A-to-D convefter usesthe samesocket (U6) as k used bt the three

I22

CLOCKS.MEMOEY.AND SOCKEIS

1 2 3 5 6

o o o-

I 9 10 12 13 15 16 17 18 l9 20

40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21

BEAL.TIME CLOCK,OPTION2

(Tothe[.lcu,thisclocklC looks usinslc Ds1202. ::lliiilftaafgli: clock implemenled like a set ol memorvlocallons.)

Nole 2 Therc are a total of si:( enpty sockets-U3, U4, U5, U6, U7, and Ult).--an the IAR-XI boa a! rcceirea. Thoughmore than one socketcan be occupiedb! an IC at anl one tine, it is best if onlj one IC is e:cperimented ithata ! one time. This v,ill ensufethat thereare no conficts betureenthe wrious derices.IJ the e{tremeright R5485socket U10 is to be used,the RS 232 IC in the socket iust to the Ieft of it, in U9, nust be renoved. One ol thesetwo communicationchipscan rcmain in place at a tines in that the communications circ it\^ doesnot confict trith thememorylocations.

Tr{ECLOCKrCS(T SOCKETU6l The two 8-pin DallasSemiconductor clock ICs areinterchangeable, andeachof them goesinto the existingemptysocketU6. The DS 1302is the successor to the DS1202. The NJU6355alsogoesjnto socketU6, but it is not pin-for-pjncompatiblewith the DallasSemiconduclor chips.Fortunately, il too needs|o haveits crystalbetweenpins 2 and 3. and its other lines can sharethe connectionsto t]rc PIC 16F877A.

SOCKETU6-HEAL.TIME CLOCKS

I23

1N4148 l

1N4148

3 5 6

U6

c3

11 12 13

c5

9qLK FIST

DS1302

frl

t5 16 17 1a t9 2A

39 3a 3T 36 35 34 33 32 31 30 29 2A 27 26 25 23 22 21

32.764KHz

FIEALTIME CLOCK OPTION3

usinslc Dsl302.(ToiheMcU,thisc ocklc f!t1ta"l,!ii1,rclock implemenled like a sel oJmemorvlocations.)

Beforeyou canusethe NJU6355.the DSI202.or the DS 1302,you haveto installa crystalbctwecnpins 2 and3 ofthc chip sockct.This hasto be a 32.768kHz crystal.rnd il is to bc inslallcdarjunpcr J5 nexr1()thereal timeclocklC sockct.If you do not have a crystalin place,theprogramwill showthe dateandotheritens on the LCD, bul thc clock rvill not moveforward. lf you want to havebatterybackupfor the clock, you needto install a batteryat junrperJ4 (at the edgeof thc boardncxt 10U I0). Thc pins tbr thisjumper arealready on thcboardwhcnyou receivei!.The IC will acceptlion 2.0 to 5.5 volts.so threeAA ccllsin scricscanproridc an incxpcnsivcbackuppowcrsourcc.(Thcpowerdrawoby this lC is 300 nano ampsa! 2.0 volls.TwoAA cclls may nol proridc cnoughvoltage bccause of thevoltagsdrcpacrcss thein line diode.soI ha!c rccommcndcd thrcccells.) The DSl3o2 (in Socket u6l The DS1302is the successor to the DSl202. Thc DSl302IC is verysimihrexceprforbackuppo\\,ercapabilityaDdsevenaddition.rl bytes pad memory.Secthc datashcct for morc spccificdetails. ofscratch

t24

CIOCKS.[Elf,OBY.Al{DSOCKETS

The emphasisin the pro$am we will develop is to seehow we get the drla to and from the real-time clock. Setting the clock is going to be done in the program sta{up routine, and the time cannotbe modified oncethe program is running lfyou want that' you can add that to the program you write. The DSl302 has31 RAM registers.Whenyou want to sendor receivedatato ihe IC. the data can be transfeded to and frcm the clock/RAM one byte at a dme. or m a bu$t oiup to 31 bytes.

TheLTC129812-BitA-to-DConverter (Also Usedin SocketU61 For our puposes,in makinghstrumentsal1dconfol lers,8 , 10', andl2_bitA_to-Dcon vertersar€use.dasinterfacesbetweensensorsandmicroprocessors.Sensorsusudly proor capacilancea.ssomeotherfactor is manipulated. vide a changein rcsislance,inaluctance, needto be amplified and digitized so they cdn very small and changes are usually These The interiace that conve s thesesnall analog environment. be manipulatedin a digital A{o-D conve(er Getting comfofiable with signals to useful {tigital information is the A-to-D conve(ers is an imponant pafi ol ma|ing instrumentsand controllers. MicroEngineering Labs provide a programon their Web site that showshow to read the l2-bit LTC1298.It's shownin Program7.4. Prosram to read lrom l2'bit LrCl298 A-to-D chip bv :9!{E$!!;g$ Labs microEnglneering ;

PICBASIC

PRO progran

to read LTC1298 ADC by nicroEngineering

; Detuae LOADER USED to a 1 1 o w u s e o f L h e b o o ! l o a d e r . nomal pr:oqrm operallon. not affect ; This witl DEFINE I.OADER_USED 1 i denne LU plns DEFTNE I.CD-DREG PORTD 4 DEFINE LCD_DBIT DEFINE I-CD_RSREG PORTE O DEFTNE LCD_RSBIE DEFINE I.CD-EREG PORTE DEFINE t|cD EBIT 1 IIICI,UDE'!{ODEDEFS. BA5" CS cK DI DO

VAR vaR VAR Vlt

PORTI.s PoR![c.3 PORTA.2 PORTC. !,

ADDR VAR BYTE

tHE ftci2ga

t2-BfT A-to.D coltvERtEn |ltso usED tN socxEf u6t

123

lo readfrom12-bitLTc1298 A-to-Dchipby .|!i9,9{iS!t:!!{l Program microEngineering Labs(Cort,ued) RESUIJT l/AR }IORD X VAR WORD

IiICH

chip select inactive set PORTA, PORTE Lo digritaf LcD R/W Line lor (ld) wait for LcD to s!ar! skip subroutines subrourine to read a/d converLer

CS

LOW PORTE.2 PAVSE 100 GOTO MAINIJOOP GETA.D:

chip select active send address / mode SHIFTOUT DII CK' MSBFIRSTI T1\1' A'DDR\3' O\1] SHIFEIN DO, CK, MSBPRET [RESItLlr\l2l ; get 12-bi! result Cg - l, ; chip seLecl inaclive RETURN .o 9e. / .dlre c-drel 0 GEII': iDDR = %00000101 ; sinerte ended, channel 0, MSBFhigh GOSUB GETAD X

= RESUIJT

;

RETT'RII

; Le

A D D R= % 0 0 0 0 0 1 1 1 GOSUB GEEAD Y = REgUt l REIURN

; sinqle

MAINI,OOP: GOSttB GETX GOSIIB GETY GOSttB GEIZ IiCDOIJT$FE. 1, 'X-", \y=t, *y, \z=n, *z PAUSE 100 GOIO MAtllt OOP END

; diff

*x,

I I

z watue

(chO = +, ch1 = -),

MSBFhish

i i , ; , ;

'

ended, channel 1, MSBFhigh

!o ge! ; subroutine ; (differentiat) GEtZ: ADDR= %00000001 GOSI'B GEEAD Z - RISULI RETI'RII

' c fLate

get z value lret y value get z value send values

lo

LCD

; do it about 10 tines ; do it forever ; end progran

a second

126

clocKs. irE[oFY. AllD socKE s

Program 7.4 reads three values from the A to D converter and displays them as X I. andZ valueson the LCD. The 1298is a two-channeldevice,andthetwo signalsare read from pins 2 and 3 on the device. The third value being displayed on the LCD is the differential betweenthe two values,meaningthat the device is now being used fbr lookng at the two inputs, not as individual inputs but as one signal aqoss the two lines (as compa-redto two signalsbetweeneach of the pins aIId $ound). The two channelsare cofirccted to the two pins at J5-Theseare ihe two pins that the crystal for the clocks goes acrossand, as mentionedbeforc, becauseof this therc is a hardwarc con|Ilct betuteenusing the clock chip and the A-to-D con'erter. The LtC 1298can providea m:L\imumof 11.1thousandsamplesper second.The device acceptsan analogreferencevoltage between 0.3 and Vcc +0.3 volts, so the sig nalsto be readmustbe conditionedto rcflectthesere4uirements.

Sockets U7 (andU8) SocketsU7 and U8 arc designedfor temperature-sensingexperiments.(U8 is a threehole group for solderingin a tbree wire temperature-sensingdevice andis locatednext in Programs7.5 and7.6. to U7.) How this is doneis demonstrated The DSI820 tenperature rcading devicegoes i socket U7. The DSI620 temperaturesensorhas to be sodered into socket U8.

io readiemperature by Usingthe Dsl 820(Program 1?j&&!!!m5{{ microEngineefing Labs)

; PICBASfC PROproqrran to read DS1820 1 wire temperature sensot ^. PORTD

DEFINE

LCD

DREG

DEFINE DEFINE DEFINE DEFINE DEFINE

I.CD I.CD I.CD ',CD ',CD

DEIIT 4 RSREG PORTE RSEIT O EREG PORITE EAIT 1

COMMAND VIR BYTA I VAR BYTE fEMP VAR WORD DQ Vt.R POR!C.o VAR TRISC. O DLDIR

;

defne

Lhe 1cd

LLD pins

allocaLe wariables sLorage for comand

alias alias

Ds1820 data pin Ds1820 dala direction

pin

U7 IANDUAI SOCKETS

i27

bv to readlemperalure Usingthe DS1820(Program lilt9.idf]lti9il Labs)(Cont ued) micrcEngineering ADCON1 =%OOOOO111 ; set PORTA and PORTE to digitaf L O WP O R T E . 2 ; lcd x/w line 1ow (v) P A U S E1 0 0 ; wait for 1c.l to start siern-on nessalre ; display LCDOUT $FE, 1, \[EMP IN DEGREESC" ; nainloop

to read

the

UAINLOOP: GOSUB INIT182O

COIAIAnD = %11001100 GOSUs WRrTE1820 = %01000100 CO!{DiAND GOSIIB!rRrTE1820 PAUSE 2000 GOSUBINIT182O - %L1OO11OO COMMAIiID GOST'BI'IRITE182O = %10111110 COMMAND GOSUBWRTEE182O GOSUBRE]AD182O

and dispLav

tenperaiure

on tcd

t h e D s1 8 02 ; init ; issue skip ron conaand ; start

lemperature

; wait

2 seconds for

converslon

to

; do another lnit ; issue skip ron comand tempetalure

; read lhe

temperatu.e the decinal ; display * 5), \ . 4 / ( I E M P . o ( T E ! ' P > > 1 ) , D E C 1 , D E C L C D O U T$ F E , \ DEGREESCZ GOTO MAINIOOP

Ds1802 and check for

inirialize ITiIITIS2O: LOW DQ PAUSEUS 5OO

PAUSEUS 100 IFDQ=lTEEA! I,CDOUE SFE, 1,

'DS182O

Set lhe data pin

1ow ho init

release data pin for hish)

{set to input

NOT PRESE!f T"

;

PAUSE 500 GOTO MAINI.OOP ENDIF PAUSEnS 400 RETURN

ldait for vrile

WRITE1820 ! F O R I = 1 T O 8 IFCOUMAND-o=0tltEN GOSUB VTRITEO EI"SE GOST'B IIRITEI

I bits

end of presence pulse

"comand" Lo a byte

byte

ho the ds1820

rra

clocKs.

MEilollY. lllD socKETs

bv i,FlQma{btls ljsingthe DSl82o(Prosamto readtemp€rature Labs)(ContDued) microEngineering ENDIF CoMMAND= CO!4!AND>> 1 NEXIT I RETI'RN

; shift

; write WRIEE0! TJOWDQ PAUSEIIS 50 DQ-DrR = 1 REl\tRN WRIBEl: Irolr DQ eNoP D Q , D T R= 1 PAusEus 50 RlruRN READ1A2O: FORr-1tO16 TEDTP- IEUP >> 1 GOSUBRE:ADBI9 NEJKT I RlrqRN READBIT t TE!rP.15 = I r,ow DQ qNoP DLDrR = 1 IFDQ=OTHEN TEMP.15 = 0

to nex!

a 0 bit

biL

to the Ds1802

; ; ; ;

low for > 60us for 0 release data pin {set to rnpul for hish) wrile a 1 bit Lo lhe DS1820

; ; ; ; ; ;

low for < 15us for 1 delay 1us at 4mnz release daia pin (set to inpu! for hish) use uP rest of line sLot fron the DS1820 tead ldperature

ord ;16bitstoa dom bits ; shift ; €reb lhe bit to lhe ; tead ; ; ; ; ;

a bit

fron

lhe

Lop of

lenp

Ds1820

presei read bi! !o 1 the tirne sloL slart delay 1us at 4mhz release data pin (seL to input for hish)

; se! bic

to 0

ENIDIF

; vait

PAusEus 50

ouL res!

of tine

slo!

RTTURN END

li!&ijiiil*i.ilFf

lo read (microEnsinee ngLabsprcsram UsingtheDs1620

This nicroEngineerincr Labs progran, too, can be found on lheir tleb site. Use the latest versron tenperaLure PICBASIC PRO proerran to read DS1520 Lhree-wire and display

tenperature

on the

LCD

socxETsuT aAltD ual

129

Labsprogramto read Usingthe DSl620(microEngineefing W (Cor nued) tempeBturc) INCI.I'DE'UODEDE!S.Bf,S'' DEFTNE LCD DRIG PORID DEFTNE I.CD-DEIT 4 DEFINE I.CD-RSRIG DEFINE I'CD_RSBIT O DEFINE ',CD_EREG POR'E DEFINE t,CD EBIT ! RSI R POREC.o DQVAR POREC.I CIIRVAR PORIC.3 lElllP VAR WORD Loil Rgt ADCON1 -%000001U Loit PoREE.2 PAUSE 100 LCDO(,!I SFE, 1, "IE!'P

; ; define 1cd pins ; PORTE; ;

} : dliqs pins : 'ese pi ' : da.. pin : lo-l< pii ; allocate variables ; storage for tenperature ; rese! the device ; set PORTA and POR?E to digital ; lcd r/w line low (w) ; wait for lcd to start j d:spl-y IN DEGREESC" sign on nessage ; foop to xead the temp and display ; on lcd

uau[t oP: RgE= 1 SEIFEOI'I DQ, CLt, Rgf-0 PAvsE 1000

; enable device I,SBFIRSI. ISEEI ; start ; wait 1 second for ; conplete

conversion conversion

to

RSI=1 sslFEottT DQ. ctK. t sBFlRsI. ISAAI ; send read comnd gHIellN OQ. CliK, I/SBPRER, IEEMP\9] ; read 9 bit temperature RSt-0 the decimal temperaLure ; display r,cDouE $FE, 1, DEC (IEMP >> 1), {.", DEC (tEMP.o * 5), \DEGREES C/ GO4IOIIAINLOOP ; do it forewer El[D ; end progran

SERIAL COMTilUNICATIONS:

SOGKETSU9 AND UlO

If all you need is a quick serial communications implementation for your project, Program8.1 (from the microEngineeringLabs Web site) gives all the code you needto reaaland write to the USART. Combine the single charactercode in a loop to read and wdte more than one character(in other words, createstrings). wilha computer) (Program to communicate RS232Communications ; rhis microBnsineeriner Labs proqran can be found on theif, web ; site. use the fales! version. CLE,AR , read and wrile hardware usart

W

DEFINE OSC 4 i 81 vaR BYIE ; BRIsc = b10111111 ; sPaRG = 25 , R c s I A = g 1 O O 1 O O O 0i Txstr = %OO1OOOO0;

osc speed initialize usart sec Tx (PoRTc.6) to ou!, re6! in set baud rale to 2400 _"i eaable serr€l po - and cor LinLous and asvnchxonous mode enable transnit

; echo received

characlers

in

e

loop

innnite

LOOP !

input, fxon serial SOSI'B CEARIN ; ge! a characler yet IF 81 : O TEEI I'OP; no character ouLput lo serial send characrer GOSDB CEAROIIT

if

anv

GO:rO LOOP

lrol usar. re ^,/e! slro ro goL preseL to no character received l F P I R 1 . 5 = 1 E E E N , lf receive flas then... char:acler co b1 81 = RCREG i set received ENDIF i

CIIARIN:

(ContinwA t3l

132

sERllL coMMuNlcATlOrlS: SOCKETSU9 AllD Ul0

(Program witha computed lo communicale l::Ptdiiallig-ili: Rs232Communications lcontinued) RETI'RN CHAROu!: IF PIR1.1T = O THEAI CITAROu ! TXREG = Bl REAURN EIID

qo back Lo calLer to send a character subroutine to usarl Lransnilter registe! enpty wait for transnit send characLer io transnit go back to caLLer

of whatis goingon, readon On the otherhand,jfyou needa greatcrunderstanding ofserial co municationsTheboard TheLAB-XIlelsus experimentwith twotypes comeswith hardwarefor the RS232standardon boardandan emplysocketthatcanbe coniiguredwith the RS485protocol(a linedriverlC muslbe ndded).Only onetype of canbe actve at anyonetime,andlhcchip ihatis not beingusedmust communications areroutedto theDB 9 female beremovedfrom theboard.The RS232communicalions connecloron the boa]d,.mdtherearePC boa]dholesfot s.three'pinconnectorat Jl0 The IC rcquiredby theRS485is the SN175176Aor equiv&rRS,l85 communications. alentline driver. are simil and,simply stated,using RS485allows you io go The two staDdards longerdistancesand the communicaiionis morenoisetolerart.(This is relatedio the capacitance of the lines usedand slrongerdriversbeingemployed.The discussionof the why andhow ofthis is beyondthe scopeof this book.) The compiler suppots communicationsto both standardsand the specifiedcompiier conmrmds shouldbe usedwheneverpossjble.Writing your own sequenceslbr controleventhoughit might be inslructive is couDterproductive, ling serialcommunications andthe hardwareyou The compiierusesthe samecommandsto accessbothstandards, put in placedetermineshow the signaLsare senlo!r! andreceived.(Takea minute to look at Figures8- l and 8-2 to seewhat the complicationsar.J.) Coimunicationsarc timed accordingto the speciiicationof the oscillator For the propertiming to be achieved,the OSC commandhasto be sct to the actualoscillator frequencyin use.Ifthe ffequerciesarenot matched,conmunicationswill be spedup or sloweddown(in spced)basedon theextentofthe mismatch.Ilyouareactudly using will slot! a 4 M Hz oscillatorandspecifyOSC20 in yourprogram,ihe communications thesystemis actuallyrunningat one-fifth downto onlr fifth thespecifiedspccdbecause the 20 MHz speed. In order to experimentwith colnmunications,we needto bc able to communicatewith to useis apersonalcomputcrsetup with a dumb The easiestdevice an externaldevice. terminalprogram.Thevariousversionsof MicrosoftOfficeWorkssoftwareall contaln a tefminalprogramthatyou canaccessanduse. Adumb terminalmay be setup by following theseinstructions: menuin your PC commandlrough,thenselect Co to the St?u]t

SERIALCOMMUNICATIONS! SOCKETSU9 AND UIO

133

Communications HyperTermi nal Iffbr somereasonHypelTerminal doesnot show up here,go to IIELP underthe Stat nenu, searchfbr "HyperTeminal," andthenclick "Finding in 2000." This will give you a window with a link to HyperTerminal. Downloads are free. Set up the HyperTerminal for 8 bits No parity I stopbit 2400ba d This is whatthe systemdefaultsto w]lh the PICBASICPROCompiler We will use thesesettingsfor all our experiments. Sct it up andsaveyour terminalto the desktop tor easyaccess. Connectthe serial cable betweenthe computerand the MCU. Since this salnecable is alsousedfbr programmingtheMCU, if you haveonly oneserialpot, you mustdisconnectit from the serialprogrammeraftereveryprogrammingsessionwhenusinga serialprogrammerIt'sjust one morereasonlor optingtbr the USB programmerThe wiring for the connectorto the serialport is shownin Figurc8.1

c6 c7

BI IN B2 IN T 1I N T2 IN

c1-

Fl OUT F2OUT T] OUT T2 OUT C2+ Q2

wirins.(Wiring lortheRS232standard diagram ilB liiii.:ali:l Rs232communications There areactualy twoRS232 drivers oniheMAX232CPE.The l/Olinesbelong unconnected to the seconddrivefonihis chlD.)

134

SERIALCOMlllUl{lCAtlO S: SOCKETSUg AND UiO

WhenandHow Will I Know If It Is Workine? Once set up properly, whateveris sent out by the LAB-XI wjll show up on the Hypellermjnal screen,and whatever is typed in at the computer keyboard will show up on the LAB-XI LCD and the H)?erTerminal screenWe will be using the hardwareserial oulput commandHSEROUT, which applies to the firsl COM poft on the LAB Xl. (TheLAB-XI hasonly oneporl, so HERSOUT2 is not applicablefor usewith thisMCU. Themosrobvioususeis for datacoliectionand conversionwith useful filtering where the datacomesin on oneporl for from an instrumeotl, is translatedand filtered, and then goeso t on the other pol1.) Let's write a simple program(seeProgram8.2), with no salety or error correc"A"s to the computerone "A" at a tion interlocks,to senda senesof?5 uppercase time with no delay betweentransmissions.Seventy-llvecharacterswill fit on one line with the cafiage return. This will keep the LAB-XI busy for aboua0 25 sec ondseverytime you pressthe resetpushbuttonwhile adjustingthe terminalsettings, ifnecessary, !lqf&di!!liFia::

to lhe to sendinformalion Rs232communications(Program

CI.EAR DEFINE OSC 4 DEFINE IISER RKSTA 9Ob DEFINE HSER 'XSTA 2 OTI DEFINE HSER BAUD 24OO DEFINE HSER SPBRG 25 IISEROUT TSD. $A, $A1 A'JPIIA VAR B{TE FOR AI,PEA =1 IO ?5 IISEROUT [$A/] NEKT AjJPHA END

speed Define the oscillator up che conrnunicaLions lsettinq and baud tale lvariables lsee PBP nanual for details l t ^o i.a .qr!. dqe set counter variable oop ro serd olr

h-

_5

A

r\a q

teeos

es

protocol,we will matchthe settingsof the HyperTerminal. For thecommunications As indicatedin the compiler manual,this is done with lhe argumentsin the HSEROUT commandand by the protocol related DEFINES in the pro$am. This is what is implemented iII Program 8.2. Before you go any futher, the preceding program must be madeoperational. Next, we need to receive information from the computer and display it on the two lines of the LCD. We will set it up so the LCD will be clearcd after every 20 characters so $e don l nrnourol ,pr,jeon line l of lhedispla).TheoPetut command recei\ed. to rcceive data is: HSERIN{ParitylEbel.

} {f iredt.

tabel,}Irt4(,...}I

wHElt a D HOWWlll I KI{OWlF ll ls wonKNG?

135

'"Timeouf' The DEFINESin the first programsegmentdefinethe variablesbeingused. "Label" are optional and are used to allow the prcgram to cofltinue if characters and arenotreceivedina timely mannerTimeoutis specifiedinmillisecondsSeethe more aletaileddiscussionin the compiler manual.In our case,the timeout meansiiat the programwill jump to the sendirgroutinewheneverthereis nothilg in the receiverbuffer The receiver buffer has preferenceas set up. However, you need to keep in mind that the receive buffer is only 2 bytes long, so we cannot linger on the send side too long before checking on the receive buffer again. Thing' lo keepin mindwhenfecei\ing informariun: I Even though certain control charactersdo not show up onscreen,ihey will still be countedas charactersunlesslhey are fillered out. I Somecharacle$ may not be implemented at all dependirg on the chdracterset recognized by the softwarein the two processors.This meansthat the filters you design haveto be carefullydesignedto takecareof all possjbilities I The receiving buffer is only two characterslong. This is a very impo(ant consideration. ellor' and'oon.and lot lransmi.siodlcceplion I weha\enottrkenan]precruliLrtls level of our expertise to cover at this get than we need more complicaled that can what we alle errors to distulb Meaning that we will assumethere aJeno hardware doing. We can write a short program (seeProgram 8 3.)to receive and display information on the LAB-XL Sincethe infonrution will be displayedon the LCD, we haveto include all rheu'ualcodelor lheI CD in uurprogram. lo receiveanddisplavinrormalion 8s232 communications(Prosram i::ni4tigifi!9il: lromthecornpuier) CIJE]AR DEFINE OgC 4 DEFINE I,CD DREE PORTD 4 DEFINE ICD-DBIT DEFINE I,CD-RSREG PORTE DEFIIIE I.CD RSBIA O DEFINE I,CD ERTG PORIE DEFIIIE 'JCD EBIT 1 CHAR VAR BYTE COL VAR ROW VIIR KEY VIIR I,ASTKEY a.DcoNl

define LCD registers

and bits

variables used in lhe rouLine storage for seriat character

BI4IE BYTE BYTE VAR BYAE

las!

= %00000111

set

key storage PORTA and POPTE to

digitaL

136

SERIALCOiTMUICAIION$60CKETSU9 A DUlo

(Prograrn to receiveanddisplavlnformalion iiqfgtl..iiil&.Ol RS232Communications (Cortlnued) lrcm thecoripuier) !o!l PoRfE.2 PAUSE 500 OPEION-REG.7 = 0

l,CD R/it rine Lot (l'i) wait for LcD to srarlup enable POR1B p!11lups

*EY=0 LASTKEY = 0

iniLialize

vars

I,CDOUT gFE. 1

iniLialize

and clear

HSERIN 1. T!,A:BEI,' TC1IART I.CDOII! CIIAR

ge! a char fron seriaL send char !o disPLaY

display

Port

'I.ABEIJ. ; get a ke\@ress if anv GOSUB CE'KEY IF (KEY != 0) AND (X:EY I= IJASTKEY) TSI:N ; send kev ou! seiiat porl IISEROUT IKEY] ETIDIF - KSY ; save last key value LASfKEY ; do it all over asain LooP Gorlo GETKIY: K E Y = 0 F O R C o L = 0 T O 3

Lo geL a kev fron ke)apad ; subroutine p r e s e t n o Kev i o , ; a1L oulput

pins

tRrsB = (DcD cor) ^ SFF ; se! one colmn Row = PoRtB >> 4 THEN GOTKEY ; IF ROWl= %0000111,1

low Pin to oucput

NEXT COIJ ; no key Pressed BETITRN ; change lod and col GofKEY! \0" ; KEY = (coL * 4) + (NcD {Row ^ $F)) + over ; subroutine RETURN ; end of Progran EAID

to asclr

nunb

Next, we combine the send and receive programs to give Lrsfull communlcatlons (This is left to betweenthe LAB-XI and the HyperTerminai program in the computer howeve! a thisl you. At this stage, you shoulalhave no problen with implementing couple of hints are Provided ) TL HyperTcrminal software lakes carc ofreceiving, displaying' and sending characters.without need for any futher modification by us. The LAB-XI software must receive charactersfrom the terminal program and dlsplay them on the LCD. lt also has to read the keyboard and send what it seesto lhe tcrminal. The receiving and sending m st be in the same main loop'

137

lrsNc IHE R!i4a5 COilMUNlCAllOl{s

LCDF^/1/LINE E2 15SHAREDWITH

u10

R]2

3 2

J10 6

B

D

-]1 ,-)o

1

t: RS485

sN175176,4

c6 c7 fiffigS slandard.)

wiring.(Wiringdiagtamforlhe RS485 RS485communications

Usins theRS485Communications standard(seeFigure8.2),pins must In orderto usethe RS485serialcommunications ground connectionsand allow J10 to carry the combe installed in JP4 to enablethe munications.As mentionedearlier. the RS232IC in U9 must be removed.After these changes,the operationswill be similar to the RS-323C standard.

USING LIQUID CRYSTALDISPLAYS:AN

EXTENDEDINFORMATION RESOURCE

General The useof LCD (liquid crystal display) modulesis coveredin great detail in this chap ter becausethey folm an important part of any project basedon the use of the PIC line of miooprccessors and the PROBASIC PRO compilers. We will considerthe popular 2line-by- l6-characterdisplay in detail, but the infomation is applicableto most LCDS on the market today. The PICBASIC PRO Compileroffers full suppo for the 2line-by-20-character display povided on the LAB-XI board,as well as for other similar displays controlled by the Hitachi HD44780U and compatjble controllers. Befor€ a display can be used,it is necessaryto tell the compiler where the display is located in momory. This is done by setling the value of a number of DEFINES that have been namedand prede{inedin the compiler TheseDEFINESlet you wrire to any LCD at any memory location in your prcject widr the compiler (assumingthereareno wiring conflicts).The specificDEFINES relatedto the control of the LAB-XI display are as follows: The DEFINES describednext are fo: an LCD confolled from PORTD and PORTE. as is the casefor theLAB-XI. Identify the polt connectedto the LCD datapins: DEFINE

I.CD DREG

PORTD

Decidehow rnanybits of datato use,alongwith tlle staflingbit. This can be a 0 or a 4 for the data starting bit, and 4 or 8 for the number of bits used: DEFINE DEFINE

IrcD_DBIT ICD_BIIFS

0 4

(o! (o!

4) 8)

Specifi the registerthat will contain the register selectionbit, and the numberoI the bit that will be usedto selectthe reqister: r39

t4O

Al{ EXIE DEDl FORilAllON RESOUBCE USI|{CUqUD CnYSlAl DISPLAYS!

DEFTNE DEFINB

I,CD RSREG LCD-RSBI!

PORTE 0

When we transferthe data,we must enablethe transferby toggling a bit, ard thc port andbit fbr dojngthis aredelincdwith the following two lines: DEFINE DEFIIIE

I,CD EREG LCD-EAII

PORTE 1

Decidewhetherwe arcgoingtoreaddatalrom,or write datato, theLCD. This is the bit, andthisbit is definedwiih the following two lincs: read./write DEFINE DEFINE

I,CD RWREG IJCD RWBIT

PORTE 2

Most of the time wc do not needto read datafrom |he LCD, so this bi1can be made andleit lowl LOSI PORTE.2

If we are,?olrrdl goirS SetLCD R/W pin to low (if writc only is to beimplcmented). r.,/eadfrom theLCD module,thepreccdingbit canbe setandleft low, or it canbetied low with hdrdware.(Doing it this way will saveoneconlrolljne on the PIC.) Sincethe PIC l6F877Ahas analogcapability,tike anyo$er similar PIC it will comeup ilr analogmodeon stairupandreset.The MCU mustbe changed10digital modeby setting the appropriateA to-D conaol rcgisterbits beforewe canusethe digital capabilitiesoI the PIC.We needthc digital tunctionsofPORTE to control thc LCD. This is donewith . a.DCONl= %00000110 This ins[uction makesall of PORTAandPORTEdigital (E00000]I1 can alsobe will providedifferentresults.For a detaileddiscussion{)1' used).Other specifications !hj.,\ee rheJrra.hecl\ecrn on A lo D co1\eriiot.. time to initializeitselfaflel startup,so we haveto wait TheLCD takesa considerable about500milliseco s beforewriting to it.Iflhere area lot of othertasksthatwill take place belore the first write to the LCD, this lime can be reduced (A trial-and error approachcan be usedto deteminc the minimum timc needed.) PAUSE500

i Wait ,5 secs. for LcD to start up

Usually, the first conmand to the LCD is usedto clear the display and write |o it on line 1,bur I am showingit astwo lines,\\,hercthe 1i$t line clearsthedisplayandthe second "Blank." line positions the cursor at the iirsl positjon on ihe lirst line and prints thc word LcDouT $FE, L

L C D O U T$ F E , 9 8 0 , ' B l a n k -

r clear

the LcD

; writlen to the 1't line ; of the LcD

1't posiiion

A11commands (as opposedto characters)sent to the LCD are precededby the code $FE ordecimal254. Somc ofthe codes;re as describedin Table 9 1.

GENERAI.

$rE,

$0X

Clear Displayshows dark 1An uncleared display rectangles in all .he spaces, which nay app€ar blot.hy and irreq!1ar) .

$FE,

$02

Go to home. Fosition

SFE,

Soc

A11 cursors slarLup.

SFE?

$08

Underline

SrE,

$0F

UndexLine cursor on s.ar.up -

StE,

$10

1 , 4 o v e -c u r s o r

risht

gFE,

$11

llover

left

sFEr

S8O

14ove .ursor

ro posirio4

one of

Line

one.

l4ove .ursoi

to Fosilion

one of

Line

tno.

Move cursor

to posiiion

one ol

line

three,

Move cursor

to posiaion

one cf

line

four.

$FE? $c0 $FE, SFE,

S91l SD4

orF. Curso!

cursor

one on Line

lhis

is

the

141

one.

delauLt

condirrion

on

0N oFr.

This

is

rhe defaulr

condiii..

one posrtion. one position.

All theseandorhefcodesaredcscdbed (sccTablc9.1). in detailin theHitachidarashecr You mustleamwherelhcscarclocatedso you can.efeftothemwhcnnecessary, Thesecommandsapply lo all LCDSusingthe Hiiachi HD4:17lj0Uconlrclleror its equivalent.Sec thc dalasheetfbr this contlollerfor morc detailedinfbrlnation.This controllerhasnany commandsnot shownherc,includinglinited graphiccapatrility (within thc characteB)andthe ability to displayJapanese kanacharactersIlis uselulto ha!e thefull40+pagcdatasheetonhand whenevefdoing anythingmorc thansendingtext to the LCD. Thc Hiuchi,l,l780 darasheei can be downloadcdat no chargefiom the following Wcb si!ci x ww\\'-alldatasheet.corn/datasheet-pdf/pdf/63673/H ITACHyHD44780.html LCD displaysrcquircthateachlinebeaddressed wirh its owr stadngposirionasindicatedearlicr Thc exceplionis thatmost l6 characldsingleline displaysafe designed suchthal the lint eight charxctersstirt at $80.andthe nexreight siarrar $C0. so thar the 16charactcrs appearto be od rwo lincs !o thc conroller thoughrheyare displayed as onc ljnc on the LCD lnodule.Also notc thal lines3 and4 offourline displaysalso havcan i egularaddressing scheme. II morecharacters thancanbe displayedon a line afe sentto the LCD. thcy \rill bc storedin lhe memoryin thc LCD andcanbe scrolledacrossthc scrccnwhenneeded. The numberof charactcrs thatan LCD canstorein its displaymcnory is a properryof

la2

USlllG LIQUIDCFYSIALDISPLAYS:At{ EXTE DEDlt{FOFii|AtlOl{ EESOUnCE

A 2-line-by-i6characterLCDmodule.(One-or twoline &!AISH!KS amounlof utililytoa proiect) LCDScanadda lremendous

the LCD asdeterminedby the maoufacturer.You canalso sdoll the display up anddown if you design the commands,and write the software' to do so This is not built into the LCD or the controllersoflwdre.A typical 16 x 2 displayis shownin Figure9 I

Usin LCDs in YourPro It is generally agreedthat most projects benefit from having a one- or twoline display incofoorated in them. Howevet these displays tend to be mther pricey (about $50) whe;provided with the necessarycontrolling IC, andquite reasonable(about $5 to $6) when bought without the supporting package.Since a PIC micmcontroller can be purchasealfor about $5, we should be able to have a complete display unit for a marginal cost of around$10 if we can figure out how to prograrnour PIC microcontrcller to con trol the display. The readily available and inexpensive2-line-by-16-characterLCD ($6 at All jn Electronics)offersus the ability to displayinformationin a limited butusefulway ourprojects.Mastedngtheuseof thisLCD displaymeanswe havegainedthe expert_ ise to write any charactetat any locatioll,at any time' or in responseto any event' this problemin detail and tells you what wheneverwe want. This chapteraaldresses you needto know analdo to makethesedisplaysinexpensiveadditionsto all ofyour proJects. _ In this chapter,you will leam how to control an LCD The code you createwill be able to be incorporatedinto almostany PICBASIC PRO programand will coIItrol the LCD from any availablehalf port (nibble)andthreeotherftee I/O lines The nn' code$ ill be mofellnraf lhanil needslo be \o ) ou canseeeraclly$ hari' going

UNDEFSTAI{DII{G THEHANDWANE ANDSOFTWANE NTEiACTIOI{

I43

but once you understandwhat needsto be done,you can write more compactand sophisticatedcodetlat will get thejob done the way you want.

Understandinsthe Hardware and SoftwareInteraction The hardwarcwe areconsidering consistsofan LCD with an integralcontrollertharis incorporated in the displayby the displaymanufacrurerIn our particularcase,rhis is theHitachiHD44780UcontrollerDisplaysareavailablewirhoutthisor anyothercon tolleri but codrolling displayswithout a controller is way beyondthe scopeof this book. For ourprojects,be surcyou buy only thoseunitsthathavethis controllerbuiltin as a paft of the display.Most do. Controllingthe displayconsistsoftelling this controllerwhatwe wantir to do. The instructionsare easyto learn and allow you to controleachand every pixel and all thefunctionsthatthedisplaycanperiorm,wiih relativeease.Youdo nothaveto read or understandthe ratherextensive40+ pagedatasheetthat Hitachi providesfor this controller,but it is well wonh thc troublerodownloadthc datasheerandsrudyit. you do not rued to downloadthis file eithet but you shouldknow whereto iind it if you needit. We will go over almosteverythingyou needto know to controlthe display asa part ofthis exercise.The exercisesat lhe endofthe chaprerwill takeit to thenext levelIn the LCD display,theimbeddedconFollerprovidesthe interfacebetweerrheuser andthedisplay.Thecontrolleris theHilachiHD44780U.This very powedulcontroller gives you completecontrol over the LCD. h allows you to addresseachand every pixel on the display.It alsohasa builtin setof ASCII characters for useby the user Our taskis to learnhow to usethiscontrollerto Dulwhatwe want.when\r'ewant.where we want,in the display. The otherconmon controller is the EpsonSED seriesconfiollcr, whoseoperationand instructionsetis very similarto thatoI lhe HirachicontrollerWe will rol considerthe EPSONconlrollerin thisbook Ifyou do decideto buy a displaywiih ihis controllerro savea few bucks,you shouldbe ableto useir afteronly a smallamounrof srudy. You will find that almost all the smaller liquid crystal displayson the market are controlled by the Hitachicontrollermentioncdearlier This meansthat onceyou learnto controlonedisplay,you cancontrolmostof themwjrh rhecodeyou create.As a mafter of fact,we will write the codein a way thai will be universalin its applicationin that we will definevariableslike the numberof characterspacesin the display and the numberof linesin the displayas part ofthe programsetup.(It is alsousefulandusu ally much easierto usethe DEFINEScreatedby the PBPcompilerto controlrhe djs play.We will le.rn how 1odo thisin a laterexercise.) The addresses of the localmemorylocations(meaningtheonesin theLCD) usedby theLCD havealreadybeenfixed,ashastheinslruclionsetwe useto write to theLCD. so we do not haveto createany ofthis rathersophisticated code.

you do needto You alonoi need the full datasheet.which is abolrt40 pageslong' bui particular display know the basic command set that controls the data tra$fer 1oyour consistsol two from and you LCD buy the provided the organization by Thi s is usually crealespecral you want 1o if only dalasheet to the or threepages.You will need1orefer The control display on tbe the like and .t,*u"t"'..,_o. if yoo *nnt to display bargraphs tobe famil don'tneed butyou the Hitachicontrollerprovidesis very comprehensive, coveredin willbe you know needto iar with it to usea display effectively. Everything you can abou!conthis exercise,but that shouldnot keepyou from learning asmuch as trolling the displays

Talkin to theLCD parameters' The precerlilg confol codesallow you to configure the display' setdisplay the charsettie shapeind position of the cursol and so on To differentiate them from or a deci' FE preceded by a hexadecimal be acter conmands, iach control code must a control will be display to lhe sent mdl 254 to tell the confoller lhal the next character resets code.After receiving one control code and its argument' the Hitachi controller to ihe datamode automaticaLly. andlowercasechamclers The controllersuppotstheASCII standardAll uppercase charanclnumeralsare supported,asale punctuationnarks andthe standad lext support acters.(The controller also suppoftsthe display of a set of Japanesekana characte$') (thoughfive It is ;1sopossibleto designyour own font for usewith the displays the inforAll be done) what can limit by seven[oi eventen] dots ;nd rwo linesdoes Greek datasheets HD4'{780U mation neededto tlo so is containedin the Hitachi m o s l 5 c i enLr[ic l o r . t u r u " , " r r u n a c e n a i nt c i e n t i f i cn o l a r i o n\i o u l d b e u s e l u aDDlications.

TheHardware Let's take a closer look at the LCD hardware. study Studv lhe datasheetthat camewith t}}e LCD. Find the pin-out descriptionsand 2' in Table 9 as shown identified them.ihe 16 pins ar" osually displays'we find providedwirh the 2-line-by-16-characier Looking at ihe datasheet poft and a few lines a have bodl if we that the c;nfiol implementation can take Place lines' predefined from any availableto control the LCD. It doesnot haveto be controlled be they can project and We can selectall the lines neededto supportthe display in our data the four/eight on any port we have available The only requirementseemsto be that paticularly line be eitherthecontiguoustop,or thebottomhalf,of a po This is not a usedif we demanrlingrequirementother lban that it meansthe smaller PICScannotbe on any will retlLriremany I/o lines in our project The other thtee lines neededcan be considering pol1 we are Since lhe same of the other ports. and do not all needto be on

THEHAFDWARE 't45

1

Logicground

2

Logic power5 volts

3

Contmstof the display,can usuallybe grounded. Fegisterselect )These are

5

Read,ll/fiie

)lhe 3 control

6

Enabe

) lines

11 '12

)8 nes ) ot daia

)hallofthepon ) canalso

13

)

) be used )seePBPmanual

7 8 I 10

) power Backlight

)Thesehvolinescan ground )usuallybe ignored Backlight

only one PIC in this book. in our casethis meanswe will usethe 16F877A.I h.tve includedthe circritry and codetbr this in the Progfam9.1 andF-igure9.1 so you caD scccxacdvwhat nccdsto bc donc. To keepir simple.lel's usePORTAandPORTB.becauselhescportsarc available on cventhc slnailcrMCLIS.andif we usea dedicared MCU ro controlour l-CD. i! will in all prcbabiiitybe a smallernoreinexpensivel8'or20-pinMCU. Let's usethclincs

Lincs | 1o3 of PORTAas lhc conlrollincsand Lhes 0 to 7 ofPORTB risthe datalines \ recanredefinetheseto be morerationaladdresses whenever$,ewant.andnoneof the pfogrammingwill haveto change.JustDEFINE what pofts and linesyou want to useatthetopofthe progmm.andthealiases assigned to their will identifythen asneeded. with this in mind. let's createthe sotiwarcto conlol a 2 line by-16 charactefdisplalr.Onccwc archappywilh lvhatwc havccrealed.wc canmigralclhc codc1()other

146

A EXTE DEDI FORIIAIIONnESOUBCE DISPIAYS: USINGLIQUIDCRYSTAL

]lole lyecouu alsousea ane Line(about$5) disPlq" brt thatflould inhibitleaming abo t goingto line 2, scn hg the disptq- up and (Iown,and sofb'lh To exryrin(:nt v itll theseJeatures,we needto haNea aisplaf Yritllat least trt'o Lines'

Settin Out OurDesi n Intent a conrrol ihc 16 x 2 displaywith a Ptc 16F877Amicroconlroller(&l3codefbr the smallerMCUSwil be the same). a Design the software so it can be an integrat part of thc softwarefor any project ^ x Use;Endard control codesso lhe project is a virtual plug in replacementfor other displays ancl in other PlCs (Only minor modifications if any will be required.) allowingthis sotlwdreprojeclto r Usi a ninimum numbelof exlemalcomponents, All we want to do is includethe of all descriptions nove betweenPIC controllers portsselccted 10 the codein our projectandconnectthe display foreverythingx Usc the projecfsregulated5_voltpowersupply trore The PIC l6F877A has33 UO hes' the displal v'ill use7 oI them' so t\te will hdt e 26 tinesleft o|erJbr ov Projact.Sinc(wedon1needdll theselines Yrecouldhare Ltsel the 16F84A. No t)rogram changesshoukl be nee(led,otlrcr than changing the litE in the DEFINES'\Nhenwe tlot' to the PIC l6F81A dn(lt)ott addrcsses

HARDWARENEEDED We will needlhe following pdts for thisprojecl: , ! x ! a ! s a t

Experimentalsolde essbreadboard PIC microcontroller:16F877Aorl6F84A Onebarc2-line by-16 characlerdisplaymodule(with a Hilachi controllcr) One4 MHz cryslal Two 22 Pf capacilors Rcgulated5-voll powersupplyfron the brcadboad Onc 470-ohm0.25 watt resistof Sone 22-gaugcinsulatcdsinglc stmndhookupwire l-kohrn 0.12 watt pull up resislor

PROGRAMMEBT{EEDED a Thc programmerncededshouldbe citherthc microEngineeng seial programmer' programmer parallelprcgrammer,or the new USB

SOFTWARENEEDED The sollwarenccdedincludeslhc PICBASICPRO Compilerandits nanual

SE'TING OUT OUR DESIGI{INTEIIT

I47

INFORMATION NEEDED lnlbnnaiionneededincludes: I LCD datasheets thatcamewirh the LCD I The PIC 16F877Adatashcct(or rhedatasheer lbr the I 6F84) We will go throughthe softwafea stcpat a time,andwhcn done.il will be yourjob to clerDup the softi\'aroandspeed p irs operadon-fof exa ptc. to optinize ir for rhc Inidurunrfoller ) nu $ ill u.e ir ) or I nroj.(r,' ' We mustpick a specificdisplayto work with so we can delelop rerl working soft wafeforit. ThedisplayIpicked sclls1br$6or soandisavailablewirh a darasbcet li.om All Elecironics. AZ Displaysalso sellsone that scemsro be identicat calledModel ACM 1602K.The shorttbnn darasheers are sinilar. but the AZ onc is in a crisppDF fomat ilnd can be downloadedfrom thcir Web sitefor frec. Doing so will meanyou canhavethis informalionopenin a wi dow on your compulcr. First,rveneed!o investigate how nranypinswe willneedon our PIC nicrocontrollcr to iDleractwith our display.This is sunnmrizedin Tablc9.3.

PINNO.

1 2 3

SYMBOL

LEVEL

DESCBIPTION ANONOTES

VSS VDD

OV

Groundfor loglcsuppy Logicpowersupply,regulaied

VO RS

5

5.0v H/L H/L

LCDcontrast. Canbe grounded H: Daiacode L: Inskuclion code H: Beadmode L:Wlitemode-Canbe tiedlowin hardware Enablesignal,pulsedifom H 10L. Hod at ll. Dalabil 0 Datablt 1

6

E

H, H>L

7

DBO DB1

H/L HIL

D82 D83

HIL HIL

D84 D85 D86 DB7

H/L H/L H/L

BL

5.0

Dalabit 6 D a l ab l 7 Plus5V Powerlor backlightinglhe

BL

Gnd

Grcundlor backllghllngpower.

10 t l

12 13

u/L

Databil2 Daiabit3 Databit 4 Databii 5

i4a

FESOUFCE Ail EXTE TEDIIFOBI/|ATION USINGLlOUlDCBYSTAIOISPLAYST

PICPIN

DESIGNATION

1

VSS

llel esnne6l€dte the l'l€

?

vDD

I'lei€er1e€ledlelhe Pl6

3

\'e

lJ€l eenne€t€dte !h5 nle

4

RS

]

RAz POITA

5

BW

2

FA3

6

E

18

7

D

B

]O

DB3

11

DB4 DB5

O

6

11

RBs " BBo '

) Halflhe poncanalsobe use )SeePBPmanual

RB7 "

)

15

BE

N6l6e1n€€tsdte th€ Plg

16

BL

lt€t oenneotsd16ihe Pl€

to lines I ' Table9.4 i ndicalesthatour mio ocontrollerdoesnot necdto be connected rvith dalal/O andnol 2. 3, 15,and 16in thal thcsehavelo do with powcrconnecliorrs ln the preccdingcase.wc will usean 8 bit databuss.and thc conneclionto the PIC 16F877Awillbe as shownir lJigure9 1. we can get by with ll lines,and possiblyeven l0 if we decjdeto do withoul the ability to readfrom the display nremory.This is not usually the case,however, thcreare ti cs whenwe needto sel lhis line high for readingthe LCD'S because busy flag in ordef to minimize lhe time usedby LCD rolrtines Nevcrtheless.\\'e car add abolLia 20-millisccondsdelay io take carc ofthe busy time Wc also necd to be able to rcad the displa, memory il we want to scroll the display up and have acccssto what is on ciisPlaylinesone andtwo Sincethis wouldbe true ibr all apPli cations,rvehaveto staywi!h the l1 lincsfor 8-bil control (Wenould not have10 read!he display if we kepl lrack of what we hadput in the display somewhereelsc in thc emory.) The cight daialincs fonn a coD\'crientbylc. andwe canassignonc of the Porlsnot beingusedlbr anythingelse.This lcavesthreelrnes:

sErrtr{G out oun bEstclt ||{tEltt

rae

I The E line, which needsto be toggled to transfer data to the LCD I The RS line, which selectsthe rcgister r The (R/W), which setsthe read/write statusofthe operations Using eight lines for dataallowsus to generateallthe codesand all the characters that the chip has in its memory, but more impoftandy, it allows the data [ansfer to be performed in one step. We can also use a 4-bit protocol and transfer half a byte at a time. Using four lines for our control schememeansthe LCD can be controlled from just one port (sevenlines will be used,leavingus one line to spare).The datasheets tell us thatwhetherwe usefour linesor eight,they all mustbe part of oneport, andif we areusingfourlines, they mustbe the cortiguousfourhigh, or the contiguousfour low, bits of a po -meaning we cannotusejust any randomlines for the databuss. The data transfer for the 4-bit prctocol must use fhe I high bits on the LCD, and \\te must sendthe datatom tlre PIC to the tlisplal with the high tu a nibble frst and the low data ibble last. This little gem is not speUedout in the instructions, btlt it's wha't mustbe done, The datasheet also tells us that t}Ie displayinitializesitself on power-up.We can reinitializeit underourcontrol,butil is doneautomaticallyon starlupandwe cannot inhibit that.All we haveto do is "not do anything"for abouthalfa secondfor the selfinitializationto complete.The busy llag is set high during startupand initialization, but is indeterminateimmediatelyafterinitializationstartsandfor 16.4milliseconds afterthe supplyvoltagereaches4.5 volfs,so we cannotdeterminehow long we have to wait afler powering up to start doing what we want. We will set a o.s-second wairpausein our progmmat startup.If that is not lorg enough,we will comeback andincreasethe waitingtime. Wait tine is a must.Ifyou do not wait, t}Iesystemwill not start up properly. Automaticinitializationsetsthe foliowing conditionsfor the display: I r r I I I I I a

Display cleared Set for 8 bit interface Setfor 1 line ofdisplay Setfor 5 x 7 dot matrixdisplay Displayis tumedoff Cursor is tumed olT Blink is tumed off Incrementbetweenchamctersis setto I (culsor movesover onespaceautomatically) Shift is off

The precedingmay not be exactlywhat we want for o r purposes,so we will go tbrough an initialization sequenceas specified by the instrnctions. We do not have to go throughall the steps,rar we rrill, sowe havea completerecord ofwhatneedsto be done for future projects. The instructionstell us thatthefollo\'r'ingsix instructionsmustbe sentto the display duringan initializationsequence. The lirst threeinsfuctionsare identicalbut require diifercnt waits after each is sent to the display.

I5O

USINGI.IQUIDCBIISTAI DISPLAYS:AI{ EXTEI{DEDII{FORIIIAIIONBESOUBCE

1A

waltfof4.1msec

2

t high

2A

waillor 100$sec

3

t high

3A

waitior 1 msec

4 5

0 low

0011xxxx

ToggleH to L

olow

0011xxxx

ToggleH to L

t high

olow

Oo1l1oxx

H to L Toggle

t hlgh

olow

00000001

ToggleH to L

0 low

00000110

ToggleH io L

Thcselnstructiorsare commandsfatherthandata,so the RS 0cgisterselect)ljnc nust be hcld high while we initialize-SeeTable9.5. nrdelajl!s follows: Thesixlincsolcodein Table9.5uc explained 00110000

"2" in a biL = don't care lhe LcD r code to initiaLize ; 3 tines, 1st trme) ; load for a comand funcrron ; wait at least 4.1ns

00110000

the LCD code !o iniLialize load for a comand function vait a! leasL 100us

00110000

the LcD code to initialize Load for a comand function liait at least l nillisecond

00 11 1 000

p,

8 o'

o!-

-.

0

1=8 bit data iranster 1=2 lines of dispLay 0 =5x7 display

road for

a connand function

(this

do

is

enLered

sEttlNGouT ouRt EstG |l{lElll

000 1 0 1 00

se! cursor 0 0 0

shift

eLc

0 =cursor shift off I =shift to rishL, or Left

load for

a comand

' Dd s p _ a y

0000 1 1 1 1

t5l

{0)

function o.bl

\--

0 0 0 0

1=culsor 1=blink load for

on so we can see lt on so we can see it a command function ' . . ' 6 6 -

00000110

r i t

e c

0 0 0 0 1 =increment cursor in positiwe dir 0 =display not shifled Load for a comand function At the end ofthese instructions,the displaywill havebeeninitializedthe way we Thereis also this businessaboutthe busy flag that we needto be thinking about. The displaylakestime to do whateverwe askit to do, and the time varieswith what we askeditto do. Wc canwait afew millisecondsbetweenins[uctions to makesure it hashad erough time for the lask to complete,or we can monilor the busy llag and as soonas it is not busy we can sendthe next instruction.Sincelime is alwaysat a premium,and we want to run as fast as we can. it meanswe must considermoni theLCD is oneofthe most toringthebusyflag. (This is impoftantbecauseaddressing time'consumingpafts of most programs,and thesesmall processorsare running at only some20 MHz.)

THE BUSYFLAG The i nsnxctionsheettells usthatthebusyllag is bit 5 at localionI I I 0001I in theLCD. Meta Codefor waiting for ihe busy bit iD |he LCD to clearis as follows:

I32

USI G LIOUIDCRYSTALDISPLAY$AN EXTE DEDII{FON AIIOTIRESOURCE

Busycheck: Readbusybyte Isolatebusybit If it is busythengotoBusycheck Retum We isolate the bit and if it is not loq we read the flag byte again We do this again andagaintill the bit goeslow. As soonas it does,we canwrite to the LCD andgo on with the program. We also have an interest in having our display be compatiblewith code generatedby the PICBASIC PRO Compiler I-ooking at the instructions for the LCDOUT conrmand' we lind that the compiler would prefer thal the hardware be set up for the following conditionsl r I I t

to PORTA.0to PORTA.3 Fourdatabits DB4 to DB7 connected Chip emble at PORTA.3 Register selectat PORTA.4 but we shouldspecifythat Two linesofdisptay areassumed,

out as lf we cannotmeet the precedingrequirement!we musl set the addresses "INCLUDE ' stateDEFINES in each and every program we write (or we can use an ment that includesa programthat doesthis for us). It's only a few linesof code,but compatibilitywith other we will haveto addthe codeeverytime, andit compromises may tum out tnat standad.It up to meet the compiler willno doubt be set systemsthat in any case, but ifit canbe you need to have this done themicrccontroller choosewill process. avoided,it shouldbe doneat this stageofour leaming The next thing we needto decideis whetherwe are gojng to uselhe soliwareas 'wherewe can an integralpart ofa prcgramthatis ronningon a largermicrocontroller useall ten addresslinesfor the display,or do we wantthe softwareto run on a smaller microconfollo thatwill needonly oneserialline to controlthedisp]aybut aledicated will have to be addedto the total projectas a part of hardwarewe design.For now' let's agrcethatwe will go with a dedicatedconlrollerjust to run the display The soft warefor tunningon a largercontrollerwill be a subsetof whatwe developso no work is lost here. The task on the input side is to design lhc softwareihat will take the serial information rcceived on one pin and output it as 4 bit charactersto the LCD with the select, rcaavwnte,andenablelines. The work neededto do readthe datain js done by the compiler with the SERIN instruclion. Program9.1 doesjust this, and is providedby microEngineeringLabs on their Web site.

ll{lEt{t sEtt[{G oul ouRDEslGt{

153

(Prosram to simulate backpack :::P.fi0iittllgitl:tlFora PIC15F84A rnicroEngineering Labsl) lby Pro program to sinulate ; PicBasic and bits ; Define LcD registers DEFIIiIE LCD-DREG PORfD j DEFIIIE IJCD DBIT 4 DEFINE IJCD RSREG PORTE ; DEFINE LCD_RSBIT O ; DEFINE I,CD EREG PORTE 1 DEFINE I.CD_EBIT ;

an LCD Backpack

for serial cha.acter Storaqe node Storage for seriaL receive sexia] Pin Barrd raLe pin 0 = 2400, 1 = 9600 data 1 = true InverLed or lrue serial

CI|AR VlrR BYTE MODE vaR BYTE Rcv vAR PoRl[B.? BAUD VAR PORTA.o STATE vAR POR!A,1

; ; ; r ;

a.DcoNl = %00000111 l,Olf PORTE.2 PAUSE 500

, set PoRTA and PoRTE to 1ow (i'l) , l,CD R/w line i/ait for LCD to slarLup ;

MODE = 0 IF (BAUD == t) MoDE = 2 ENDIF

;

Set

node

;

set

baud

digital

TEEN

(STATE == 0) IHEN MODE = MODE + 4 ENDIF

rate

IF

r,cDout

$FE,

L

LOOP, SERIN RC{/, MODE, CEAR LCDOUT CEAR GOIO IOOP END

; Set

invelled

or

true

and clear

i

Initialize

; ; , ;

serial Get a char fron Send char to display over again Do rt all end Progran

displav

input

but it canbe usedon the 16F877Awithappropriate This programis for the 16F8,1A, manytimesbeforenow,so lhis shouldnot be DEFINES.You havesettheseDEFINES a problem. The precedingproFam is for a 16F84APIC. tf you loadthis pro$am into the PIC, you canconnectthe 16F84Ato the LCD, dndany serialinformationthatcomesin on PORTB.Twillbe displayedon the LCD. Now you canconlrolthe LCD from oneline on the main processor(The selectedpin doesnol haveto be PORTB.7.Any tree pin canbe specifiedasthe input datapin in the pfogram.) The wiring diagramfor the 16F84Ais shownin Figure9.2.

i54

USlt{GLIOUIDCRYSTAL OISPLAYS! AN EXIEI{DEDINFOnMATIO nESOURCE

o

u""o

EEVOO

--

--:: ftft ftft

Yq :*

E E z

E E E E o

E E E -

o

:liFlSillqi**i:l wiring diagram:LCDbackpackusinga PIC16F84.{Thedalacanbeprogrammed to comein at anyfree line.11doesnot have10be on pin B7,Youset lhe lineyouwantio useIn Program 9.1.)

LiquidCrystalDisplayExercises Theseliquid crystalexercisesareto be performedon the LAB-XI board. l.Write a programto put the 26letters ofthe alphabetandthe ten numeralsin the 40 spacesthat are avai)ableon Iine l. lnsert four spacesbetweenthe numbers and the alphabet to fill in t]}e four remaining spaces.Once all the characten have . been efltered,scroll t}Ie 40 chamclersback and fortl endlesslythough lhe 20 spacesvisible on line l. 2. Writea programto bubblethe26 capitallettersof thealphabettbrough thenumbers 0 to 9 on line 2 ofthe LCD. (ThismeansrFirst,put thenumberson line 2. Then,"A" takesthe placeofthe "0" and all the numbersmoveover.Then,the "A" takesthe placeof the "l" and the "0" movesback to position 1 and so on till it getspast the L Then,the "B" startsit way acrossthe numbers,andso forth.) 3. wdte a program to write the numbers0 to 9 upsidedown on line L Wait I second and then flip the numbersright side up one by one. Provide a time delay between chanses.LooD.

LIOUID CNYSTAL DISPLAY EXERCISES

I55

4. Write a progmmto identifythe buttonprcsscdon lhc bullon pad by displayingi|s ro\l'nnmberon line I andlts colunn on line 2. Idenlily eachline so you know whal is bcingdisplaycdwhcre.Scrollthetwo liDesup e\'erl tine a buttonis pressed.Add delaysin |he scrcll so you canactuallyseethe scrollingtakeplace. The full insrucriontablefof the LCD is shownin Tabie9.6

COII,IMAND R

R - - - - - OATABUSS- - - - - -

s

w

7

ClearDisplay 0

O

O 0

0

0

0

Cursoral

0

0

0

0

0

0

6

0

5

4

3

2 0 0

1 1

0

DESCRIPTION

0 Clea|sdisplay & relurns

EXECUTIN TIME

1.64msec

1 address0,Alsoreturns lhe displaybeingshilled to lhe or ginalposilion, DDRAI\,4 conlenlsreman

EntryMode 0 Set

0

0

0

0

0

0

1

t/D s

l/D:Selcurcofmoving

40 psec

l/D=1:lncremenl l/D=0:Decrement S: SpecifyshiJlof display S=1:Thedisplays shiJied S=0:Thedisplayis not shiifed Display ON/OFF Conirol

0

0

0

0

0

0 l

C

B

Dlsplay D=1:Displayon 40 Usec D=0iDisplay otf Cursor C=lrCursoron C=orCursoroll B nk B=1:Blink on B=0iBlink otf

Cursor/ Display shifl

0

0

0

0

0

1 S/C R/L x

x

lvovescursofor shiilsihe displayW/ochangng DD BA[,,]conlenls S/C-0:Cu|s0rshlft (RA[,4 unchanged) S/C=1:Display shill (RAlvlunchansed) R/L=1:Shllt io ther Shl F/L=O:Sh lt to the lelt

D

40 lsec

i56

EXTENDEDI FOFiiATIONRESOUBCE

USINGLIQUIDCBYSTALDISPLAYs:A

COIdMAND

F

R - - - - - OATABUSS- - - - - -

F w z o s I

Set O 0 Funclion

0

SetCG BAIM o Address

0

0

sei DD RAM 0 Address

0

1

BusyFlag/ 0 Address Read

1 B F

Wite Data

1

0

ReadDaia

1 1

r

z l

ol

DESCFIPTION Fosc=250KHz

EXECUTIN T!ME

Setsdatabusslength(DL), 40 !6ec # of dsplaylnes(N),and characterlonts (F) dols DL=1:8bils F=0:5x7 DL=o:4bits F-1:5x10dots N=0:1 linedisplay N=1:2lnesdisplay 40 generator SetsCG BA['4address 1 Character dalais sent CGFA['4 (CG)RAMaddress aflerihis andreceived nstruction 40 psec SeisDD RA[,laddress. Displaydata(DD)RAM is sent DD Ramdata address address/cursor aiterlhis andreceived inslruction 40 | Readsbusyflag(aD and Addresscounierusedlor addresscounlerconlenls bothDD& CG RA[rl or 46 lsec WdtesdalalnloDDRAIV Writedala CGRAM ReadsdalalromDDRAI\'4 46 Readdala or CGRAM 01

DLN

F

x

x

"lmageslnc sI" of Table9.6 is fof the 16 characterby 2-lire LCD displaysolclbv alldis thenroduleusedin all rheprecedingexperNew Yorkfor about$10pluspostage, hasoncfor 56' related diagramsAll Eilectronics imeDlsarrdihoscsho\\'nin ftc pfecedirg schenc packs usethe Alnost all LCDSwith back

ustNc sENsoRs(TRANSDUCERSI

General Beforeyou canmakea decisionaboutmodifying an existingcondition, you haveto sense what the curent condition is. An awful lot can be donewith the five senseswe all have, but for many other things that arc important in our everydaylives we needhelp. We get this helpfrom electronicsensors.Thesesenso$convertthe informatiol in the sysleminto infomation we can absorbusing our five senses.The preferredsensoryinput in humans is visual and auditory,but we often alsousetouch.smell and tasteareusedlessoften afld are usually reservedfor organicinputs, sometimesthoseindicating a hazardor danger. The following are someunusualexamplesofhow we useour five senses. I I I : I

Sight Hearitrg Touch Sm€ll Tast€

Aulomobile traffic is conlrolled basically by drreecolored lights. Theele\atorbeckon.uswrtha ping. The cell phone vibrates (if set to do so). presence. Gasolinecontainsan additiveto helpus detectits dangerous The DEA agentcanrecognizecocaineby its taste(at leaston TV).

Whenwe think aboutsensingsomethingour humansensescannotdetect,we are usually thinKng about signals that, to us, are weak or hard to difierentiate in the ambient noise.Thesea.resignalsthat needto be filtered andamplified andthen conveftedto signals we cdr recognize.As you readthis, a few hundredtelevision and radio broadcasts arc zipping past your brain that you are completely oblivious to. If you know what fre quenciesto look for, how to filter out the signal you want from them, and then how to presentit to the humaneye and ear,you could watch and hearthe databeing broadcast. Cablenetwork subscriptionsseemto indicate this is wo h a lot of money every month| Thus, there are four main aspectsof sensing. of the existenceoithe signal. I We musl havea knowledgeandunderstanding I We must find a filter that will isolate and identifv the sienal. t59

a6!

USINGSENSORS(TMI{SDUCERSI

I We mustamplify the sigral if it is weak. I We must convcrt the signal to accommodatea human sense,or transform it into somelhingdelectttble by a machineor instrumcni.which we cantheninteractwith. Oniy thenarewe in a positionto makean intelligentdecisionaboutthc signal. Onemoreimportantthing:We needto havea very goodideaofwhat we arelrying to do in orderto makesurewe end up with the signalwe areintcrcstedin. lt won r do to havean insll-umcnlthal tells us the humidity,lvhenwhat we werere.tllyinteresred in wasthe tempcralure. The world is full ol nuny exotic and interestingthings to experinenr with and deted. butin ihesediscussions we will concentratc on thosethingswe mighifind in an everyday cngineedngschoollaboratoryor amatcurengineer'sworkshop.We will not discussany thingfor whicha sensor itselfcannolbe puchasedfor lessthanlj30(U.S.dollals).Wewill stickto usingonly a few sensors andemploythen in manydillbren!ways.The sensory detectors/transduccrs we seleclmustbereadily availablcandbe ir?rerl.i."-dblewirh a small microcontroll$ Evenso.othereffots nust be undcrtakenbelbre we havea viableinstrument or controllcr somethingwhich we will discusslalcr in Chapters15 to 22We canno!do anythingaboutthesignal.howcver,if we don't know whereto find it or know that it evenexists-The signalalsonust havea sensorwe can se,that will respondto it, andit ispreferablethatthc sensorrespord only tothe sjgnalweareinter estedill- All otherresponses dcrractlron the raskar handandcanbc considersdpart "noisc." general of the Someof lhe most exquisitelysensitivesensorsarc biological.The dnrennae ofthe moth canrecognizethe pheromones it hasevoived1()detectin the pats per billion or less.Thesescnsorsarc so sensitivethey can evcn dclecl the gmdient in the scent, allowingthenoth to movetowardsits lalger.Hereit is importanrtonotethatin a three dimcnsionalspace,onepaftin 1,000,000,000 mearNthaithe noleculesbeingderecred are 1000molecrles apart-Sincctheantennae aremanymillionsofmolcculcslong,quite particles possjbly afew are bcingintercepted aranyonelime at thescsccninglyminuie (We arcjust beginningto seethe useolbiologicaychenicalelenents concentrations. in our mostsophisdcated aDdcuttingedgeelcclric/eleclrcnicinstruments.) In mostcases.we areinterested in linearspaccralherthantlxee-dinensionalspace, asmentionedeadier Inrnostcases, ifwecan delectabout1paft in 10,000,we arequite happy.One part in 10,000refersto bcing ablero detecta changeof 1 part wirhin rhe entirerangefrom I to 10.000.To useareal-wo d example,considerlhe cor1lmon voltmetet which candetectliom 0 to 1000volts with a sensitivityof 0.1 volrs.This is rhe approximate rangeofour mostcommoninslrumcnts.but olcourse we usebothmuch coarserandmuch iinel instrumentsalso.Thc lollowins lists somecommonexamDles wc areaUlamiliar with. Oven thermometer

0 to 000 dcgr(cs

15 degrees

Oral thermometer

95 to 105degrees

0.1 dcgrccs

Housethermosfat

32 1()132deg€es

I degree

Car speedomet€r

0 to 120mph

2 mph

1S... tHE MOSTBASTC OUESflON WEilusl ANSWER

l6i

Car odometer

0 to 999,000miles

0.1 milesfor shortdislances

6-inch ruler

0 to 6 inches

1/32inch at besl

Steeltape

0 to 96 inches

1/16inch

M€chanicalstop watch

0 to 30 minules

0.05seconds

we will in theuseofsensorsthatconnectto microcontrollers, Sincewe areinterested restrict ouNelvesto thosesensorsthat provide an electrical signalor a signalthat is easily convefiedinto an electrical signal. Signalsthat dre easyto interfaceto a microcontrcller aresignalsthathave(changing)electricalpropertieslike... I I I I I

Resistance Voltage Capacitance Reluctance Frequency

What competencies mustbe masteredin orderto createmiooconfoller-basedinstru mentsandcontrollers?Basically,you have a signalthat must be transfomed into a reading oi some sort in a one- or two-line display, or something similar What you must masteris the processbetweenthe two. Thus,the tasksinvolvedbreakdown tbis way: l. Understandingthe problem (this is much more important than it seems) 2. Capturing the signal 3, Filtering out the part you want 4. Conditioning the signal to make it acceptableto the PIC 5, Converting jt to a digital format 6. Manipulating the digital data to createa readablevalue 7. Doing one or more of the following: I Displayingthe valueon the LCD I Transmitting the value to a computer for collection and storage I Turning extemal device(s)on and off as necessary Essentiaily,the chapten in this tutorial are devotedto thesetasks.

TheMostBasicQuestion We MustAnswerIs... u hy \\ouldTwanrro buildan in'rrumenl when instruments to measuealmosteverythingI am interestedin are already available off the shelfl

t62

US0|GsE|{SORsITnANSDUCERSI

The answerto this questionis neithersimplenor short. Firstf Almosl all the instirmenls you needdre ,rot aNailableotf the sheA.Morc acarrately stated,only bits andpa s of the insmrmentsyou requir€ a1eavaiiable.The instrumentswe will build will be more useful than their genericoff-the-shelt'siblings, and in someways aremorespecificallytargeted10&e taskat hand.Sincewe lnow exacdywhat we need,we will designan instrxmentthatprovidescxact\ what we want.We do nol have to compromiseon any prope(y of the inslxment. Also, our instrumentswill be able to provide other inlelligence functions, like turning other laboratoryequipmenlon and off as neededby our experimenls,and as determinedby the condilions the insirument is monitoring in real time. This is a vsry useful featurealmost neverlbund on an ind slfial instrument,but that is absolutelyessenlialif we want to autonute our prccesscs. Second:We will be ableto automalicallyscndthe informationbei g galhercdto a compulcrfor analysis,eitherin realtime or on a defbr.edbasisdependingoDwhal our overall needsare,We canalso gathefa lot moreinfbrmation over a longer period of time with our custominstrumentsbeca se we will now have the ability to automatethe process.Transientphenomcnathat requireconstantmonitoring ovet long periodsof time cannow be monitorcdcontinuouslyand andproduceonly in a few importantinstances intelligentlywithoutconcemor addedexpense. Third: Our instruments willbe ableto makeintelligentdecisionsin realtime.Ifdata the instrumentcan call pointsthat are unexpectedor extraordinaryare encountered, this to our attentionso remedialor special(evenhuman)attentioncanbe givento the Fourth: Or the outpulside,the ability to turn pumps,fans,healers,andthe like on andoff automaticnlly, basedon lheinformationsensedby theinstrumentcannotbe discantum an ancjllarypiece missedour of hand.Verylew oft:the shelfvolt-/ohmmeters of equipmenton or off at a given voltage.Most do not evenhavean oulput that we could it will be connectto if we so desired.However,wilh our customdesignedinstrumenls, easy,Few ohmmelerscansendthe value readto a computu every secondor every hour. But with theinsfumentswe will build,jt will be easy.No olf ihe-shelfi nshxmertucan thatwe inBASIC with oneclick ofthe mouse.With lhe instruments be reprogrammed The instruments we shall design and build will create,however,this will be the case. will be intimatelyfamiliar to us, so modityingthem will be relativelyeasy.Oncethe input-output appurtemnceshavebeendecidedon and connectedto the microcontroller, therestwill be controlledby thesoftwarewe will write.llwe feelthe instrumenlis not respondingthe way wc want it to. we can modify it with minimal effort. Fiffh: Specialized instruments canoftenbe madefor a lot lessthanyou may thinkl vouwilldevelop critical skillsyou ca usethe resto^'orr lifu. This in itselfmight Si\tht (After all, wc live in the information age,no?) b,r more important than anything else. We can say with some confidencethat with a liltle learning and efforl on our part, wc arl]cancreateinsiumentslailoredto our necdsthat will help us be morc produclive. (And in the processmakeour livesmoreinferesting.) So whatkinds of thingscanbe sensedeasily?We needto know what we cansensc becausewhat we sensewill bc the datasourcewe feedinto our microcontroller-based instrumentcontroller.

tYpEs oF sENsons

rc3

Typesof Sensors lnexpensivesensorsarereadilyavailablefor mostofthe following: I Humidity I Gravity r Level I Acceleration I Resistance I Capacitance I Voltage I Frequency I Magnetic field I Hall effectsensor ! Pressure I Altimeter r Vacuum I Distance I Sonic I Themal I Infrared I Temperature I Light I Chemicalsensors tPH I Sound I Noise I Soundpressure I Contouror roughness r Speed r RPM I Position I GPS I Orienlation : Gravity sensorsfor two and three axes We will, of course,useonly a coupleof thesesensors because our interestis not primarily in the senso$but in manipulatingthe informationwe getr?m the sensors, no matterwhat lype ofsensorsthey are.In orderto do that,we mustleam how to effectively connect to whatever is provided to us and provide outputs that can control the deviceswe areintercstedin manipulating.One chapterin this book is devotedro making the connections on the input side,while one concemsmai:ingthe connections on the output side.In the eight projectswe will undertake,rhefollowing sensorinterfacingprob lens will be addressed:

164

Usrr{c3E s('ns fiMt{SDUcERS)

counting the frequencyof a pulse train Creating accuratetimed inte als (frequencies) Exploring various counting techniquesand how lo implement them Readinganalogsignalsanddisplayingthem 4. Dual thermometer Providing a stablehorizontal surlacewith an unusual 5. Artificial llorizon instrument Making controlpanelsthrougha usefultechnique screen 6. Touch contoler Controllingonevariable(derivedfrom item 4 of thislist) 7. Single-point g. Solarcollector Exploring data collection over a long time period; data logging

I . Tachometer 2. Metronome 3. Marblescounter

Theseeight projectsare designedto familiarize you with the basictechniquesneeded andon hobbyto bnild instrumenhandcontrollersin today'sengineeringlaboratories

You Two InterestinsResources Will Want to Investi ate Radioshackhasasensorslearninglaboratory(-$50) thatprovidesan inexpcnsiveway to accessa family of sensorsthat canbe usedwith our instriiments. The Mccraw-Hill book tlectftnic Sensorsfor the hil C€rius discussesa numberof interestingsensorsand explainshow to usethem. Thesetechniques,and othe$ lhat are modifications of tbem, can be usedin the instuments and controllers we shall cleate.

CONDITIONING THE INPUTSIGNAL

General Filst, we need to get a handle on the signalscoming into our insEuments.This chapter cove$ the techniquesusedto collect andcondition ihe ilput signalsso they canbe connected!o the microcontroller. Beforc we can do useful work, we needto detectand managethe signal wo areinterestedin. In our particular case,there is the addedrequirementthat the signal either be an electrical signal or be such that it can easily be conve ed into an electrical signal. Though a Bourdon tube prcssue gaugemight rcad the pressue just fine for most engineerirg applications,we needa pressuresensorthat providesus with an elecldcal signal we can feed into an electrical instrumgnt.We are not so much concemedwith the magninrde of the signal as we are wifh knowing it is iII a range we can read, manipulate, ard bring into our microcontrollers. A linear signal responseis most desirablo,but we can take care of the nonlinearity of a signal in oul controller with software if that becomesnecessary. In the engircering laboratoryand amateurengineer'sworkshop,the electrical signals we encounterwill most likely be somewhgrebetween0 aDd 120 volts ac and between 0 and 24 volts dc. No matter what the conditions. extleme caution and care should be exercisedwhen dealing with any kind of electrical signal. Electricity canbe lethal if not handled with care. When you aie dealing with the higher cur€nts and voltages, seek the help of an experiencedelectriciar if you feel the leastbit uncomfo(able wiih undertaking that part of the task. Be informed that certain work must meet the rcquiements of the National Electrical Code in most judsdictions, so help from an experienced person(electrician) can saveyou a lot of time and headaches. Let's take a look at the ac signah nrst, and ihen we will look at dc signals.

166

COt{DlTtOt{lNGtHE tt{PUT StGt{AL

Alternatins CurrentOutline a High voltage I20 \,olts(we will not consideranythingover 120volts) ! Low voltage 24 volts a Electronic(computercircuitry signals) Lessthan24 volts,andusuallylessthdn or equalto 5 volts

ALTERNAIINGCURREiIT The signalswc are interestedin as they rclate io the electrjc grid and laboratorydevices will mostlikely eithd bc al24 voltsac or at 120voltsac.Chanccsaregoodthatif we got it ffom arythingconnected to thc nationalelectricalgrid,it will be in lhis voltagerange. Evcrything undera half horsepowerthat canbe pluggedinto an electrical sockctis likely to be at 120volts ac at 60 Hz. The conlrol wiring mostcomnonly usedin thc United Slalcsis at 24 volts ac (butsonetiDeshighervoltagcsareused).Certairstallers,rclays. andcoilswill use24 voltsandwill needa transfomcrto cleatethisvoltage.Look lbr this lnnsibrner andactuallyrneasurethe voltagesat thc devices.Control wiring doesDotusuallyhavelobcin cond itifit isat24 voltsor b€]ow(ch,rcktheNationalEleltricalCode). Ifwe wantto interactwith a controlsignal,we mustextendihescsignalsfrom thedevice to our controller, conditiorl it, and fced it to the microcortroller. (Output to things needlaterin theChapter12.) ing 24 voltsdc or 120vollsac is discussed property in is the frequencyof thc signal.A ac elecrrical we arc intercsted The other numbcrof instrumentswe arc interestedin arebascdon how often a signalchangesover ape od oftime, eitherat a fixedrateor a varjableratc.Variablentes are usuallyrcad with countersoveranextendedperiodoftime, while fixcdratescanbereadovera very measurement ofone cyclewill suffice.The meas shoftperiod.Oltcntimes,theaccurate uremertofpulse rvidthsis a mixed bag ir that we measuethe limc betweenchanges ofa fixed signal. cornputet tnput If we are gcttinginformationfrom a computer.we will needan intcrfacethatmatchestheoutputoI thecompulcrbothat lhe voitagelelel andasa communicaiionprotocol.Thesesignalsarealmostalwaysat or under12 volts.

LrrrectLuffent uutllne a I | t

24 volts($c will not coveranythingover24 voltsdc) 12 volts 5 volts 3.3volts

DIRECI CURRE T The signalswe arc interestedin are under24 volts,but beforc you do anythingelse you shouldcheckthis lor yourself.lflead acid batteries.rre involvcd,it will probably

s[f,PLE SW|ICHESAt{D OTHERCOI|T CTS

i67

be at 12 volts-Most automotivevolragesarecurrentlyat 12 volts (themeasuredvoltageoDa chargedbatteryon a runningcar will be slightly higher).Heavy dury trucks o{1enusetwicethisvoltage.Ifyou areconsidering elcctronicdevices,the voltageswill probablybe belween3 and 9 volts. Conditioningdc signalsfor inrroductioninto a microprocessor is usuallya matterof makingsurenot too muchcunentor too high a voltagegoesinto the electronicswith appropriare resisrarces andbuffcrs. Note SdJ&ry isdlnd)l "JOB 1." Be cautionedLhat||he wo*ing aroundleadacid batteries, extremely larye currents (well oyet 50A amps instuntuneousb) are easilJ areilable dt the baxery temtinals.Thesehigh cuffents ca be tlengerousdnllirill easily melt wiresand eren wrcnches. Be wr)" careful whenw)rkin] dround lead ddd battefies. Ifyou are notfaniliar with hazanlsassociatedwith bdtteries(acids and hJdrogen),),ou shouAt1:1ke the timeto becomeacquaintedwiththisaspectof your h,otkforyow o',\,ns.letJ, and the saJetroJthosearound)ou, beJorcJou start. A1l the signalswe collect must be condirionedand convertedto a fbrm thar the micrcprocessor cansafelyaccept.The conversioninto digilal formatcanrakeplacein the microprocessor itself, so we do not haveto worry aboutany extemalelectronics to do that. We havetwo interestsin the incomingsignal.Wilh dc signals,we want ro know if the signalis on or ol-f,andwe want to know its magnitude-(dc signalscanalsocone in as a squarewaveor a frequency,which is coveredunderac.) On off inlbrmationis usedasa meansofderectingwharrhc conditiotsdownstream liom usaresowe cansendcontrolinfbrmationto whati s upsfeamfiom us.If a device that is interactingwith us hascomeon, we needto respondto it in a specificmanner, meaningthat the informationshouldbe usedaspan ofour controlfunctions. Magnitude information is usedto determjnethe condition of the signal we are moni toring, to know if we aregetting the reslrltswe want. If we drerying to maintain the tem peratureof an oven, we needto know the nagnitude of the signalcoming 10usacrossthe thermocoupleso we can conveil it into a temperatureand thencomparethai temperature to what was needed,in order to decidewherherto turn the heatingelementseither on or off. The insoumentwe designmanipulatesthe thermocouplevoltagedata,to comprehend the information in thc sisnal. and then makesthe dccision that conrrolsrhe heaters.

Smple SwitchesandOtherContacts KEYBOARDS The readingof keyboardsand othermatricesof switchesis coveredin grearderailin the earlierpartoflhc tutorialunderkeyboards.

BELAYS A relay can casily be usedto provide a dry contacrthat can be read wjtb thc PlC. Thesecontactsare quiaenoisy (electrically)and shouldbe debouncedeither with

t6a

cot{DllloNll{c THEl PUr SlGl{AL

a latch hardwareor softwareas they arc read.If two pins areavailablefor the signal' that a advantage the have Lalches can be set at one pin and clearcdwith the other' We attentionany more need turclea "ignal ia;bes immediatclyaltd then doesnot is shown circujt cancomeiack to it whenconvenient.A signallatchingandclearing in FigureI l.l.

RES|StAilcEs canbe rcadby placingthemacrossa referencevoltageandgroundand Potentiomcters techniqueis using one of the analoginputs 1o readthe positionof the wiper' This a poten project where final in the inputs and dem;nsrated in the chapteron rcading tiometeris usedas the setpoint determiningdevice can be readeitherby measuringthe time it takesto dischargea Fixed resistances techniqueused known valuecapacitolor by comparingthemto a known resistor'The js explainedin will a"pendon ttrenat,reoithe resistorbeingread The iirst iechnique places the PBi manualunderthe POT commandon page116 The secondtechniquc the wtper the two resistancesin seriesand thenreadsthe middle voltage as it represents powcr the across to shot likely are resistaoces in a potentiometer.The cautionis that low well over to be needs resislors two supply and grounA.The total resistanceof the 2k ohmsandis bettcrif ovet 5k ohms.

5VDD

A PUSHBUTTON SWITCHORTHE DRYCONTACTS

10hoHN,ls

SIGNALLATCHES ONTOPIN1 AND!S WITHP]N 2 CLEAFIEO

ittriiitt€rllr.lli

sisnallatchingand clearing.(Readinga relayor a prrEh-

bullonwiiha laich)

ctRcutTRYFoR coltDtttoN tc Dc stcltlfs

Circui

169

for Conditionin

24-VOLTSIGNALS Signalsbetween 12 and 24 volts dc can be introducedinto a PIC by creating a voltage divider to reducethe signal to approximately4.5 to 4.9 volts dc as shownin Figure I L2. A currentlimiting rcsistor of between220 and 1000 ohms is placed in serieswith the sigml as a safety precautionto limit the cuffent into the PIC. The PIC inputs are high impedanceinputs but it doesnot hul1to add the rcsistancein an experimentalsituation wherethings might tum out to be not quite what you expected.

r 2-voLTstcl{als Signals at 12 volts can be handled the sameas the 24-volt signals above with appro priate resistancesFovided, or ihey can be passedthrough standardlogic components to conditionfor usewitlr a PIC.All signalsshouldgo thoughconditioningbuffersor gateswbenthereis any concernaboutthe qualityof the signal. The PIC pins are in a high-impedancecondition when programmedas inputs andwill acceptanyTTL or CMOS level signal,so the taskat handis to convertthe incoming signai ifto either a TTl-'level signal or a CMOS-level signal. Floating signalscoming

100KoHMS

15 KOHTVS TO 20 KOHNTS

l:tlli{di!:]t1a:: wiringdiagramfor readlnga 24-volt stgnal,

116

coxD|rr6t{|llc

tHE tI{PUt glGl{AL

into floatinginputssiould havea pull-upresistor( 10to l00k ohtns)at thepin to tie the pin high.Optoisolato$canbeusedto isolatethenoisysignalelectricallyftom thePIC If you haveanisolatoravailable,useit whennecessary. The dia$ams in Figures11.3through11.6showvarioustechniquesthat may be

5 VOLTS

gre

signal. ot inco.ing 12-vott Optoisotatton ANYSUITABLE BUFFERWITH CI\,IOSORTTL OUTPUT

5.VOLT LOGICINPUT

$voltTTl-levelsignals.

X3ffi

HEXHIGHTO LOW LEVELSHIFTER LIKETHE74HS4O5O

1s-VOLT LOGICINPUT

ANYSUITABLE BUFFERWITH CI\,IOSORTTL OUTPUT

clFcullnY Fon GoxDltlox|l{o Dc stclttfs

2 TO 5 VOLTSAS NEEDEDBY THEGAIE

5 VOLTS

1oKoHr\4s

3.VOLTLOGIC 3-volt signals.

OPENDBAINOUTPUT SIGNALTO PICINPUT FLOATSANDCANBE PULLEDUPTO VOLTAGE NEEDED

l7l

CONDITIONINGTHE OUTPUT SIGNAL

General The microcontroller we use will eithcr be a TTL- or CMOS level inpui/output device Its signals can be jntroduced to other similar devices,almost alvr'ays,without altering them.However.therealworld is not full oiTTLand CMOSdevices,andwe will have to connect to motors and relays, Silicon Controlled Rectifier (SCRS)and TRIode for AlternatingCunent(TRIACS),lightsandpumps,anda hostof otherequipmenton our bench tops and in our laboratories.This chaptershows us how to take the TTL signal as il comes out of the microcontroller and prepare it to inform and control the real world. The types of deviceswe will be sendinginformation to can b,3broken down into the following: Computers I Serial interfaces r COM1 I COM2 r Parallelports are more complicatedto useand will not be discussedin detail (Today,they are not often usedfor interaction wilh MCUS.) Inductiveloads I Motors I Relays I Solenoids Resistiveloads I Lighr butbs I Heaters

't?4

col{DlTlol{ll{GtHE oulPUT SlGl{Al

COMPUTEBSERIALII{TERFACE The PIC family of mi croconlrollerscan sendinlbrmationto. andreceiveinlormation from, a compuier.This canbe aloneseriallyandin thc p allel mode lt is mucheasier io uscserialcommunicatios, which is covercdin detailin Chapter9

COMPUTERPARALLELINTERFACE SomePlCs proviclethc abiliiy to createa slaveparallelporl On ihe PtC 16F877A, PORTDis uscdfor rhis.while PORTEis uscdto controlandmonitof datatransLr containdetailson usingslavepoftslbr theseinte|faces.but they are Thc dalasheets with a a1lhelevelollhis texl andif all you want 1odo is communicate not Decessafy jntedace We will not cover PC, by far the easiestway lo do so is with a sedalRS232 parallelport commuricationsin this book

INDUCIIVE LOADS Any time we aresendingan clectricttlsignalto an irductivc dc load' we haveto make to absorbthe Ilow ofenergy reteasedwhen the inductiveload is disarrangements conn;cted.The easiestway 10do this is to prolide an aPpropriatediode that will ofl-era safepath for thc reversecurrentto dissipalc The diode is installedso it is conductingin th,3directionoppositcto the normal flow of currcnt Altach the cathode ofthe diode to the positiveterminal,ard the anodeto the ncgativelerminal of ihe induclive load as closeto the load as possible-In this posiiion. no currcnt will ilow ihrough the diode when conneclcdacrossthe dc voltage,bul when thc device (rclay, solcnoid,analso on) is disconnccted,the reversecurrent ftom it will flow acro;sthis diode andbe dissipatedin thc deviceilself. Diodes nust be selectedto matchthe expectedload amperageand voltage Thereis no harm iD ltsing a djode that is larger than needcd.

RESISTIVELOADS directly throughsolid staterclays(SSRS)thal will Resistiveloaclscan be connecteal acceptTTllevel signalsandthatcaltcontrclanywherefrom l0 to 40 ampsat 120volts ac d;ecdy. TheseSSRsarc thc intedacesofchoiccfor connecdngthcseloadsbecause thcy are easyto useand all lhe internalclectronicwork is alreadydone for us (see Figure 12.1).Someof theseunits evenhave a tiny LED built into $em lo indjcate wien they areactive.(Dcvicesollcn turn o1Tandon whcnthe ac voltagegoesthrough the0 voltagetransition,soyoumustmakesuretheloadvohagewill actuallygothrough 0 volt, or the devicewill/may nol switch.) Selccta unit specificallysuitedto the task you have in mind lrexpensive unrts are availablefiom mosl supply housesselling surPluselectronicequipmenton fie Internel.I myself have purchaseduscdunits and have ncver reccivedonc that did

fryWl A sotid state retay.(Thesesotid staterelaysprovidethe easjestway10connecllo highervoltages. NoteLED.) If you aregoingto rxn a motoror oiherinductiveload,makesuretheunit hassuitablesupprcssors built into it or pmvidefor the suppression of the transientsyourself. You canalsoisolatethe PIC from the Ioadby usinga solid staterclay to controlan apprcpriatelysizedmechanicalrelay,which in tum contols the motor.This schemo would not be suitablefor loadsthat wereto be cycledmorethanoneor two timesa minute.Youwill bum therelaycontactsout if theyarenot overly oversized.

AN INTRODUCTION TO THE EIGHT PROJECTS

TheWebSite Use the suppon Web site. It is an important paft of all the information you have access Lo with this tutorial. Specific to the following chapters,it has exrensivepictures on it thatshowhow all theprojectswerebuilt by me,andthesecanbea tremendous helpto you in building your own projects, even if you decide ro moalify and extend the proj ectsbeyond the minimal and basic construction I have undertaken.Thc pictures are in color and color addsa lot of uscful information.

t Techni You mustbecornecomfortablewith eight basictechniquesto be ableto designandbuild instrumentsand conrollers tbat canmonitor or conrrol the variablesandprcpertiesyou havean inGrestin. They are t. CouDtingsynchronous andasynchronous pulses. 2. Creatingaccurateshort andlong-timedintervalswith rimers. 3. Usingcounterseffectively. 4. Sensingandreadinganalogvoltages. 5, Usingpulsesto controlexremaldevices. 6. Creatingsinple scanningroutinesto monitorphenomena. 7. Conholling the propety or function you are interesredin. 8. Logging data over an extendedtime period automatically. The eight basicconsrructionsin rhis tutorial cover thesetechniquesoneat a rjme. The projectsaredesignedro giveyou anexpansiveview of themanypossibilities thatusirg

175

TOTHEEIGHIPNOJECTS AI{ II{IFODUCTIOI{

what They sclectivelydemonstrate offersyou. thc experimenter. PIC micrcprocessors andengineeingstudentwith fai y mjnjmal canbe doncby the anateurexpedmenter resources. This is an introductorylulorial, as opposedto a highly lechnicaltrealment andare you mighi find in a morc rigororsiext. The projcctsarefairly straightforward you and give you need to create your and the confidence hodzons designcdto expand you They demonstrate wanlto undertake. neoessary for thework buildthc instruments avariedapproachto a seeminglyrandomsetofproblems,whichwhenseenasa whole, give us ihe expericnces we needto movc to thenext level,whichis ofcoursethedesign requircd. andconstructionofthe instruments The eightinstru cntsare: lnstrument Name l. Tachometer 2. Mctronome 3. Ma$le counter 4. Dual lempcraturesensor 5. Aftilicial horizonrable 6. Touchscreen 7. Single-poinlcontrollef 8. Solarcollector

Function ReingSfudied Courting pulscs(synchronous) Timer tecllniqucs (asynchfonous) Couniingtechniques Analog{o-digitalconversionconsidenlions Convertingpulsesto Inotion A uscfulreal-worldscanningapplication Controllinga "set point" processwith details Dala loggingovertime

you mlrstmastefto lechniques Thesccight projectsreFescntthe eightfundamental you Each instrumenl in the series need. andcontrollers be ableto build the instruments jsolate problempart conversion of lhe datacollectionor andaddressonc is designed!o proce€d with thc techOncewe undcrstandthe basiccomponcntsin thesesystems,wc can Decessary ior the tasksit hand. niquesnecessary to designthe Plc-basedinslruments ininto As alwals. thelirstthingwe musldo is to convertlhe signalwc areinterested a uscabledigitalformat.Oflen.you may need!o amplify the signalbcibreconverling it to lhe digitalformatrequircd. lhe oounlingofpulses l. The lachometerprojectis a basicexercisein understanding you (It how to usescvensegvarying rates. also teaches tharcancomein at widely mentdisplays.) 2. The mefonomeshaveto do withlearninghow to usethetimersto createaccumtely we createwill opefateidenlically,but will usethe timedintervals.Thc metronomes varioustimersto crealethc intervalsneeded.This is adetailedexerciscin the useof limcrs in the PIC 16F877A.Both the LAB-XI and the tachometercrcaledearlier wilycan be usedto createthc metronomes. 3.In the marblecounterssertion.we will leam aboulgood.bad,and ambigltoussignals,andexperimentwilh someofthe techriquesuscdfor sofiirg thingsout with a as we collecl the data.Thesecounlingtechniquescan and will be micrcprocessor applied 10all sorts of instrumenlsthat yo createin the future. 4. The two thcnnometerinstrumentallowsyou lo measurelwo q antitiessimultane_ but theydo not haveto be.Onc can alsobe designcd ously.Both aretcmperaturcs, youcrealc andtheinstruments to be a setpoint.This is thebasicinstrument/controllet project, signal conversion wilh lhc appropriate be varialions ofthis will csscntially

THEErcHr'ECHtl|OIEo

lilg

modulesadded.Lateron in Proiect13.7.we will convertthisinstrumentinto a con trollet andthenin Project13.8we will useit to log fhe dataftom a solarcollec|or that the two quantitiesconover an extendedperiod.It is importantto understand sidereddo not haveto be the samething. We could usethe linear brightnessof a light to control the pambolic speedof a motor by putting the information though a custom_ designedcontroller 5.In the artificialhodzon project,we leam how to usepulsedsignalsreadfrom a sensorto contol the position of a table positioned with 1womodel aircraft servos. The seNos arc fed signalsthat are a flrnction of the eror signal readfrom the sensor andhold the tableiII a hodzontalposition. 6. Building the touchscreenis the basisfor leamingaboutscanningroutines.Though andleam aboutthe lechniques thisis a relativelysmallsurface,we candemonsuate usedto make a touch screenwith this project. A touch screenis a control panel you can make on the laboratory bench with minimal cost and cffo( 7. The two-input controller is a finished instrumentthat incor?oratesthe competencies learnedin thepreviouslymentionedprojects.We thenusethisinsFumentin thenext project to createa data logger g, Dataloggingis coveredin thecontextof a solarcollectoraDdusesthetwo-inputconfoller to provide the data that we then ]og over an extendedperiod of time automatically. The dala will be sent to a personalcomputer for storageand go through eventualanalysisat a laterdate. we willdiscuss,thenbuild, Addinga little nore detailtotheprecedingdescriptions, and hopefully understandthe engineeringand sciencebehind the following eight projects.

l. THE BASICSOF COUI'ltl G PULSES: THE IACHOMETERPROJECT Researchhas indicated that carefully managing the engine speedas you drive around town cansubstantially increasethe efficiencyof your automobile.Designandbuild an inexpensivetachometerthat canbe addedto an automolive enginewilh minimal effon. Designrhe deviceto displaythe enginerpm (revolutionsper minute)on a four-digit display.The displayand the CPU boardare to be placedat someconvenientlocation in ftont of the driver The systemmost use the I2 dc power available on the automobile and sta when the ignition switch is tumed on. This is an exercisein countingpulsesthat comein at vanousrales,and dispiaying theresultson sevensegmentdisplays oron anLCD. Almosfall the sigoalsweusewilh microprocesso$ endup havjngto do with countingandnanipulatingpulses,so this is you musrmaster a corecomperency

2. THE METRONOIIIE!CREATINGCO TROLLEDPULSES Ms. Music, our local high schoolmusicteacher,did not get thefunding lbr themetronomes shewantedfor her class.The principalhasaskedyour electonics instructorso seeifhe/she can qet the classto create25 low-cost netmnomes lbr the music students.

iAO

TOTHEEIGHTPBOJECIS A|{ II{TBODUCTIOI{

The elecronic netronomeis an exerciscjn creatingaccuratetimeintervalsthat are on boththc LAB-Xl boa1dandthetachometerboad. trom a potentiometer controlleal programming for botl the LCD on the LAB-XI andfor a disexercise includes The LEDS used on the tachometerin the first 4 seven scgment play consistingof the

3. COU TING MARBLES!DlSCFlMlilAtlNG BETWEENvAR'lflllc PULSEDSIGI{ALSAND FEEDINGTHE TIMER/COUIITERS Part 1...Mr. Marblssthe managerol the local marblefactoryhasbeenplagucdwith the headofthe electronicsdepartnent marblecountirg problemsandhasapproached The classis chargcdwith design inexpensivc solution. to seeifhe cancomeup with an go ing a marblecounterthat countsthe marblesasthey by single file at the .ate of about rcnmarble\persecond.JndlhclrclorymJnagcr\\dnl'lLrinclca\elhrlralea accupossible.The counterthatcancountthehighestnumberof marblcsjn 10seconds ralely will be selectedas the instrument of choice by the plant manager jnforThis is aboutleaminghow to countthe pulseswc encounterwhenprocessing mation,Somecomein slow.somecomein fast,somecomein vely fast,andsomeare hardto discrimioatefron the backgroundnoj se.This exercjseexposesyou lo lhesereal world problems. Part 2.-. Mr Marbles. our friend from the marble factory. is so happy wiih the per_ fomance of the counterwe madefor hi m edrlier that he hascomeback to us for an even "Wha! can you make in the way of a rcally fast counter?" he asks We faster counter haveconvincedhim thatwe canmakehim whathe wouldconsidera reallyfastcounte! but the marblesneedto go by singlefilejust asthey did for the previouscounters.To this he hasagreed. This insfumentwill counthow manycommoneverydayglassmarblesgo by its so calledgate.We aredoing thisjust to do ill Someonemightjust havea usetbr this, or the detection,amplia modifiedversionof this, but our purposehereis to understand ficadon.andthe counlingofsmall seeminglyrdndomsignalscomingin helterskelter' In this experiment,things startto get complicatedandwc haveto useour wirs to figurc out how we cansohJetheproblems.So,in a way,this is an exposureto ihe reaiworld.

TWO AI{ALOGS|GI{ALS 4. rHE DUAL THERMOIITETER! AiID DISPLAYED TO DIGITAL COI{VERIED Dr. Thermo is in the piocessof undertakinga large researchproject to check the energy transferacrcssa largenumberofcoils to be usedin the air conditioningindusty He hasindicated that he needsto know how the lemperatureoI the air and the temperature of thecoolingbrinechangesastheheatexchangetakesplace.Designan instrumentto display the inlet tcmperalureand the outlet temperaturefor both fiuids sinultareously The instnment is an elecaodc themometerthatre3dstwo temperatures Thisis ani nstxmenlyoLrcanuseeverydayin yourday to-daymonitoringof thesystems amundvou. Eachsensorcostsabout$3. This exerciseis aboulreadinganalogsignals,

THEEIGH' TECHNIQUES IE1

converting them to digital format, ard then interpreting them for display on a twoline liquid crystaldisplay.With this instrumentyou candeterminethe energyllow in most systemsif you lnow the mte of flow a the nass propertlesof what is going by. you will needto mastertoprccessanalog This projectcontainsthebasictechniques to digital signals. signalsas opposed

5. AN ELECTRONICARTIFICIALHORIZOI{;SOPHISTICATED INSTRUMEI'ltSMADE EASYWITH MICROCOiITROLLERS gravily sensorthat indicatesthe changein gravity in Parallaxsellsa very interestiDg both the X andY directjonsas well as the ambiert temperatureat lhe instmmentas (We will nol se the temperaluresensorparl in oul experiments threefrequencies. ) with a surynsinglygoodresolutionof The sensorcanserseup to 2 Cs of acceleration 0.001G (a milli-G). We will usethis deviceto createa lwo axistablethat stayshori' zontal while the surfaceit is mountedon is turnedevery which way (within aboul 20 degrees)relatjve1othe horizon. we will beusingis theMemsic2125.TheParallaxcompanydeliv The accelerometer ers it alreadymountedon a tiny board with pins at 0. 1 incheson center lt plugs direcdy into an experimentalbreadboardwith stdndard0. I inch on-centerholes.Thete are o y six pins, and two of them are at ground! Threeother Linesprovide the tbreefiequencies we areinlerestedin, while the sixthpin is the powerpin. How simplecar thisget?1 The signals from this sensorare in the fonn of frequenciesthat vary wiih the tilt of The sensoris most the sensorin the X andY direction(andthe ambienttemperalule). held vertical.We when the sensor axis is and least sensitivc sensitivenearhorizontal. give they us the signalswe need themso cantal(etheliequenciesreceivedandprocess to controla coupleof hobbyR/C servos.The linkagesbetweerthe servoandtableare to be arrangedto keep the lable approximalely level. The final correctlon can be providcd in softwdre with a tookup table but that nay not be necessarydependingon how we designthe softwar€l

6. THE IOUCH SCBEEI{ The touchscreenteachesus how to scana nurnbelofsignalsto decidewhat needsto confolled by the signals.Uselultouchpanelscanbe cre be doneundercircumstances atedto simulatethe operatioDof conuol panelsfor electrcnicdeviceswith minimal expense.Inthis exercise,we createa touchpanelthatcontfolsthe blinkingrateoftwo LEDSanddisplays&e conditionsat the panelon the LCD. Simple touch panelscanbc placedi n front of simple graphicsto createthe inpuls we needto control the instrumenl and controller we are building.

7. THE FII{ISI{EDCONIROLLER In lhls project, we convert the two temperatur€themometer into an adjustablethermostat with an exlemal inhibit capability to demonstrateour ability to createa confoller/

IA2

TOTHEEIGHTPBOJECIS Al{ INTRODUGTIOII

A. LOGGINGDATAFROMA SOLARCOLLECTOB sensor, we addcom unicationsto it and Now thatwe havea wo*ing lwo-lhetmometer createa systemthat logsthe conditionsinsidea solarcollectot to a PC. automalically everyminute(or anothertine interval)for a ycarA largepoftion of the trtorial is devotedto cachoneof lhc precedingdevices,and of lhc theoryandthe programmingtech buildinginsnuctiorNaswell as a discussi(nl each chaptcr niouesusedareincludedin

Notes In the iollowirg cxercises,wc will rely as much as we can. on the capabilities of the PIC and try to do the projects with as few exlcnal componenls as possible to keePour costs down and to increaseour l(nowledge of using the PIC 10 do whatevcr it is capa bleofdolng. Forexample, inthe lirst project, the tachometer,wccould easilyhaveused ICs thal convert BCD (binafy codcd decimal) dala to whal is needed by the seven segmentdisplays to display a number. but we did it without the ICs to leam how ihis can be done with the PIC alone. On the sollware end, we rvill use as few of the iDstructionsfrom PROBASIC as possible to keep the cmphasison thc design of thc instrnnenls as opposed1()masterirg the tricks and techniquespossible with the extensivc software language The emphasisis on thc PIC and what is inside it STOPI STOPI STOP1STOPI STOPI (}NCEIN A LIFEI'IMECHANCE TO EXERCISEYOURWITSI Younotrbave! rareopponunilytoerercise)ouf crcalivethirKngl Nowdratyou knowwhdtNe wi1lbebuildiDg,loucan i)ldeaseshar you willSet iioD these substanlially e{ercises by notreadin8tlD folldvitrgp.goslar a couPlc abouthow of daysandspeidirytimefiinkin8 scriou$lv you wouldusethercsoutlesdvrilabletoyou Lodesien i! thischaptcr lhe iNtumenLsdescribcd Makcdrawings.ndslethes of whatyou sould do in yourshoplog.Latc!,it sillbe instuctn'elo coDparc thc $ith how I havcdescribed \rhatyouenvisioncd Hopetiilly,{hatyo! coire upwift (in at instrumenLs. leastsodecrses)will be norelnspircdLhanfte offerediDtris lLrtorial andtecliniqucs simflinedniethods Goodluck

THE UNIVERSALINSTRUMENT:

A BACKGROUNDDISCUSSION

The Propertiesand Capabilities of a UniversalInstrument What are Almost all the instrumentswe will makehavesomesharedcharacteristics. anddisadvantages do we get from lhem?Whatdoeshaving theyandwhat advantages and our instrumentsbasedon PIC microcontrollersdo for us?Askingthesequestions unde$tandingbasic conceptslike thesemakesit easierfor us to proceedwith our work. Let's look at the propertresneededin ar instrument by comparing it with an instrument we are all familiar wjth; a volvohm meter or VOM. We will compareits properties and functions lo the insfuments we are designing to get a better understandingof what we a-retrying to accomplish and how we might accomplish it. musthavefhe iollowing basicpropefies: Eachinstrumentcontroller I . lt must have a way to enter infomqtion lnto rhe device in a convenient manner.In a VOM, we are Fovided with two probesthat we place at various points in the cir cuitry.In the instrumentswe make,we will providecomectionpointsfor the signals and pulseswe are interestedin reading, but more importantly we arc interested in providing inputs that canbe programned ro influencethe operationof the instrument in rcaI time. Wirh a little imagination, the inslruments we create can be both interactive and intelligert2. It must have someform of decision making cqability that allows it to manipulale the jnformation sent to it, and someof lhis capabilityneedsto be conffollab]e (influence-able) bythe operator.IntheVOM, thereisa selectorswitchthat we use we will usethe comto chooserangesandfunctionswe will use.In our instruments, puterto set the parameterswithin which our instrumentwill operate.we will be able to progam the instrument for the task at hand as needed.For our instruments, ta3

tA4

DISCUSSION |NSTBUiIEINABACKCROUI{D THEUI{TVERSAL

the computeris the selectorswitch! (Note that in the newerVOMS, someauto rangingcapabilitiesareimplementedfbr selectingtherangeusedby thlrmeter'The in the display output,loo.ls rangedso it canfit in the limited numberof characters To us.this meanssomeoflhe decisionnaking we mighthavcundetakenhasbeen buill into themachine) Theflexibililyoforr. hrtr&m?rrs to theintelligence rclegated is rcotedin the abilily Io reprogramlhe instrumenlwilha few keysrokeswhenever In ofderto be ableto uselhis flexibility,we mustdesignthe hardwarefor neealed. our instmmentsiDa lvaytharwill lenditselfto softwarcnodificationwjth relaiively minimalcffort in arelalivelyshorttine. we hare to think aboutwhatthc insnxmenv controllerwill/can do as wc designit so it will pedormits intendediunclionswith keepin mind thattheinstrumentwill do only whatwc design someelegancc.Always you must@ mit thisunrcp! toYur broiir' It is v€ryimportant ir lo do. 3. The devicemust havea wi\y ro ot\tPl|litlforndlion in a usefulformat The lbrmat CRT display On canbe anythirgliom a simpleswitchclosurclo a comprehensivc the VOM, a few digits sufficeto givc us ihe informatjonwe need.On instrumenls the addilionofa two line displaycanprovidea con basedon PICmiorccontrollers, sialembleamountof infonnation. The many outputport lines canbe usedto tum LEDS on and oli and to provide other on/off signals.A serial port can be usedto sendand feceiveinformationfrom a computerAudio signalscan alsobe added.Versatility will be our slrongsuit. 4, The infornalion/outputdesiredshouldbe ableto be.rldrilirzl for a while sowe can collcctit. Someol the newerVOMShavea storagefunctionthallcts you freezcthe displayat selectedpcakvaluesor al sclectedtines. Our instrunentswill be ableto do that and se the information to a computerat selectedintervals for storagein that computer1ofacilitale fulure analysis.Thcy will be able to makedecisio s in real tine whenwe arenot therc.andtakecorrecdvcactions,or summonhumanintervention. The capabilitieswe can incorporateinto our instrumentsare limited only by our imagination.wc arethe designcrs.

A B asicTemperature-Controlling Device lhisin theconlextofa simpletemperaturc-corollingdevice.Late! Next,we will discuss we will actuallybuild this device. ofan instrumentthatcanbe described What arethe basicpropcrtiesandcomponenis single'pointconlroller?Basically.thefollowingfunctionsare asauniversalall-purpose called lbr: I ! ! !

Sense condition Seta point ofconirol Compare&e ptecedingtwo ilnctions Outputa sigsl

A BASICTEMPEFATUNES.COIITFOLIING DEVICE

IA5

Let s go over them one at a time. l. A simpleuniversaiconlrollerwouldallowusto controionesetpointor propcrty.For thepurposcof thisdiscussion, we areassumingthisis a tcmperature. Theinstrument musl allow us to controla temperature. In orderto do this, it must havea connection fbr the temperature sensor,andwha! we providewill dependon the sensorwe haveselected.We will usean LM34 temperature-sensing IC as our detector.This deviceusesa threewirc connection.so we wili providea threescrewtcrminal1br 2. The devicemusthaveanadjlrstable senirgvariableofsome sortto which the above temperature is to be compared.This is the outputsetpoint controldevice.Fot our insfiumcnt,we will useapotentiometerOncervchavethetwo signalsin ourinstrumentworking,we canmakeadecisionas lo whetherwe wantto turn on the heator thercfrigeration.This will be determincdwilh the softwarewe will write to control the instmment.(The potentiometer is a thr€e-wirevoltagedivider thatwe wiil use to parallelihe input thatthe lempeiaturedetectoris providing.This isjust like what we discussed earlierin thisbook,andwill makethe comparisons casiex) 3. We needa wry to tum the actualinstrunentfunctionon andoff. Tbis swilchis not the on/o1T switchlor theinstrumentb t anotherswitchthatallowsus to activaterhe portionoflhe instrumentwhen operational we arercadyto startrheinstrument.This switchletsusplay with our setupandgeteverythingj ustright beforewe activatethe instrument.Asinple SPSTswitchwill be adequate forthis andwe will usea small toggleswitchforit. Sincewemaywanttomountrhisswitchat arcmotelocationlor someof our applications, we will connectihe switchto theboardvia two sctewterminals.The majoriuncdonofa switchlike thisis to allow our insfument to be controlledbyanolherelectronicdeviceI This is a very powerlulcapabilityandis rhefirst stepin the extendedautomationprocess, 4, The controlierneedsa coupleof connectorsthat the outpursignalappearson. We will connectthe controlledmachinecompoDent(heater relay,and so on) to thjs point.Ifwe haveto ampljfy theconloi signal,this is wherethe relay(ransislor)or whateverwillbe connected.Ifwelatef wanttoreversethe signalliom nomrlly off to normallyon. thisis whercwe programthe logic to do so.This is theoutputof the instmmcnt.We will annunciaterhe signalwith an LED andusetwo screwrenninals asthe connectionpoints. 5. The instrumentneedssomesortof indicatoron ir to tell us whentheoutputirom thc instrumentisactive.Thisis aconvenience itemthatmakestheinstnrmcndconfoller moreuser-friendly. Wc will addan LED toindicatethison ourconffollerWhenthis LED is on, the instrumenlis puttingout a signalat theoutpulconneclors. This LED alsoletsus see&e instrumentoperatingwilhouthaving10connectup to areal control point.andso on, The prccedingdescribesalmostall instrument/confollers. No matterwhar you are askrdto control,the instrumentyou designwill havethe precedingbasicmodulesor conponentsin somelbrm or anoaher, Il may controlonefunction,or it may controla hundredfunctions,but eachfunctionwill suppot the previouslymentioncdabilities.

ta6

DISCUSSIOI{ tHE uillvERsA! lNslRuiilEl{t A BAoKGROUNO

ea ier is anextensionofthe themomeierwe will coDstruct Thecontrollermentioned is covercdin detail pro.jects. construction lts in oneof the

Notes hardwareandsoltwarecomponents'so lhey All instrumentsarc assembledfiom slanda-rd nodule in the instrumentprovidesonefunction Each a modular structure. tendto have you wouldfind on systensbascdon thePIC commonmodules Thefbllowingarc some l6F877A: I t r I I I I I I !

Analoginput section MathemalicalmaDipulalions Set the DEFINES for rhe LCD Displayto the LCD or two Reada potentrometer (CRT) Displayto displays Reada keyboard Put out a tone Reada s{'itch module A communications

by sclectingordesigningthemoduleswe needaDdassemWe createour instr-Lrments you canuse you havecreateda nodulc or subroutrne, projectOnce into a bling them to olher transportable you it to be easily your if oreale designs it againand againin again. in you agrin and a lol oI time' will savc designs.Takingthe time to closo now Notice in the projeclsthat follow that I too uselhe modulesover and over agaiD' I also maclea concertedellbrt to useas fcw instruclionsin PIC Basic Pro (PBP)as possible,so the emphasiswas on the designof ihe insfuments,not on fancy software lricks and routines.

COUNTINGPULSES:

TACHOMETER A PROGRAMMABLE

ProiectI In thj s first project, we build a programmabletachometerthat can delectbelween I and 9999 pulsesa second(or anothertime period) and display the resultson 4 seven canbe countedin two ways.Ifwe know segmentLED numericdisplays.Thesepulses we aregetting a fixed duty cycle squarewave,we canmeasurelhe total length of a pulse and detemine the frequency of the signal from that. If the pulses are not coming at a regular rate, we can actually count the pulsesover time anddeterminethe rate ihat wayWe can write the softwarefor both techniquesso we can seethe difference.At the end of the project, we will take the sourceof the pulsesinto considerationand discusshow to modify the software to display an actual rpm (revolutions per rlinute). when working with miooprccessors, much of the infonnation we deal with is read are miooprccessors andthe like because andprocessed aspulses,counts,frequencies, vdlues. So il becomes digitaldevices,andareusuallynot designedfor handljnganalog impotant that you be comfortable with gathering,processing,and displaying infbrmation of a digital nature, and this project focuseson that aspectof our knowledge and understandingregading microprocessors.Onceyou arecomforlablewith the designand consfuction of this tachometer,you will be able to handleall otherfrcquencyinput projects with confidence. We will usethe LAB-XI board as a helper instrument as we go along. Fhst, we will makethe softwarework on the LAB-XI (when we can) andoncewe know we canrcad, count, and display the inputs the way we want, we will move on to the fabrication of LED basedtacbometer showr in Figure15.1. the seven-segmert In this project, the LAB X1 will be particularly helpful becauseseven-segmenldis playsrequirea lot or wiring (that cango \\'ong) andit canbe dillicult to get things sorted

147

taA

PULISES! A PROGnAiIABIE TACHOMETEF COUNTIIIG

i:t!!!i-iltfgif::

tachometer. A programmable

out at times.Whenusinga LAB-XI, we know we havea workingplatiormto develop the softwarewithout having to worry abouthardwareproblemsthat we might have cre ateallor o rselves.After we havethe tachometersoftwareworkng. we canusethe LABXl to createpulsesgeneratedat known frequenciesto check the accuracyof the instrumentwe created, dispiayshasto do with leamjng The displayingof the countson 4 seven-segment is, ofcourse'mucheasier displays.It used and inexpensive commoniy how to usethese but in this exercisewe the LAB Xl, 2 x 20 LCD on to displaythe informationon the platlbml. If you prefer the proj will be using th.- LAB-XI only as our initial software -X you will missout on the expeect caneasily be modified to rul1on the LAB 1, but then rienceoflearninghow to usethe sevensegmentdisplays.In anycase'the PIC we use will be lhe l6F8??A.(This PIC will be employedfor all the projectsin this book' and the LAB X1 will be usedto suppoft all the projects as needed) The facl that we ar€ using only four displays is becausethe integer math provided in thecompiler canhandleonly 16 bit math(65535max),which limits us tofourdisplays if we want to go to a 9 in the Left-mostdisplay.It also simplifies our problem at this stage analwill demonstratethat refreshinglbur di splaystakesus to the ma,\imumthat the PIC can confol (at 4 MIIZ) without having to useassemblylanguageprogrammjng lt is also a compronr.isethat has to do with the fact that four digits can be handled easily with onednda half pofts (12lines.|. We will be using a small dc motor with a 2o-slots-per revolution encoder(available on it asour signalgencrator(seeFigure I 5-2),but from my Websiteencodergeek.com) before we do that we needto undertakesomegeneraldiscussionabout counting pulses "counts/time penod" are.If you have and what the problemsrelated with low and high someother device tha! can generatepulses,you can use it if you like.

PROJECT'I

ta9

A small dc molor with open encodersattachedfor generatingsignal pulses. (Fewer encoder slotsgiveyoumoretimeto counithem. givesfullaccessto electrcnics.) Openconslruclion

Figure 15.3 shows a circuit used to make a simple and inexpensivepulse generator with a PIC 16F819.This device can be usedto generatethe many pulses and intervals neededfor the numercusdevicesthat will be created.The fact that it is programmable is the key. No program is provided becauseyou now have the skills to program this devicefor the outputsyou need.The following areacouple ofhi s. The tlree pin oupur canbe programmedto emulatean R/C hobby output,while the 5 volts that a se o needs are provided at the middle pin. The five pins connectedto PORTB shouldbe pulled up, and then as they arc shortedto ground with jumpers, they selectthe type of ouQut the signal generator will create. Use the three LEDS as indicators to show you what is goilg on in the progran Figure 15.4 shows a picture of the nnished device. Bare boards and kits for ihis are available at encodergeek.com.

PULSERATE|LOW RATECOI{S|DEBAI|OI{S Let's thini( aboutthis iII termsof a smallencodedmotor like the oneshow! in Figure 15.2. First, lefs look at what the problems at the low rpm end of the spectrumare. Let's assumewe are looking at signals coming from a rotating shaft and want to know the speedof the shaft in rpm. The lowest speedof the shaft is 1 1p,t(revolutionsper second) andwe want to updatethe rpm display every 0.25 seconds.We needto be ableto detect at leastfive countsevery0.25secondsto indicatethatthe shaftis tuming.If the shaft had 20 markerson it. we would have to look at the shaft for at least0.25 secoDds to get thesefive counts. We need a certain amount of time to prccess and display the information. so the count needsto be read four to six times a secondif we are to meet our minimum specification. We have agreedthat there are 20 markers on the shait of

i90

TACHOMETER coul|rl c PULSES: A PROGRAMITIABLE

A2

vss

BO B1 92 B3

VDD B7 B6 B5 B4

circuildiasram. i:i!!!.!!!.ii:tf{gl Pulsegenerator

this molor. We c:m read thesewilh a photosensitivedeteclor, and the output from the detectoris suitablefor direct input into our PICMCU. This is a reasonableass mption in that mostphotofansistorswill feeddhectly into a PIC pol1 (The encoderon our motor meetsthis specification.) For low-speedaccuracy,the 20 markersmust be placed accuratelyaround the shaft At high rpm, this would not natter becausewe would be readingmanyrcvolutions every 0.25 secondsandthe relativeplacementof the 20 markersaroundthe shaftwould be jntegratedout over trmc, We can usethe COUNT commandin the PBP languageto do the counting-For a period,the commandwouldbe: 0.25-second coul{r PoRfa.2, 250, lfl sherePORIA.2i' lhelineIhe5rgnili. .jomingin on countinginterval or 0.25'second 250 is ior a 2sO-millisecond placed in will be IV1is lhe variablethe count

PFOJECI I

j$!!i!i-lild€{::

t9i

Photoof pulsesenerator

ofthe The PIC will acluallytake 0.25+secondsto executethis command(because counting time specified)and there is nothing elsethat canbe done while this command is beingexecuted(because of the way the compileris designed).Sincewe could get a feel for the rpm in a much shortertime at hjgher rpm, this can definitely be considered a low-rpm problem. The sollrlion to this low count sjtuation is to have a higher count encoderon the shaft so a large number of countscan be interceptedin a shorl pedod of time. However,as we will see,thereis a trade-offat the high speedend when we increasethe encodercount.

HIGHSPEEDCOI{SIDERAIIONS There is also a limit to how high the frequency can be and stilt be in ihe range that drc PIC canrespondto. For the PIC 16F87?Athat we are usingin combjnationwith the PBP software,this frequency is 100 kHz for a 20 MHz OSC and25 kHzfot a 4 MHz OSC(ow case).If we wereusingan encoderthathad 1000countsper revolution,we could keep up with a shaft that was rotating at 25 revolutions per second. 2 5 , 0 0 /01 0 0 0 = 2 s A motor running at 3600 rpm, which is quile common, spins at 60 revolutions per second.We can seethat we starl to exceedthe limit of what we can do rather rapidly.

192

COUtltl G PUISES:A PnOGRA|I|IABLEtACHOfllEtEn

So on the one hand,high-count encodelsare desirableat low speeds;on the other hand they becomea prcblem at high speed.A corcllary to fhis is that it is very difiicult to run a shaft accuately at low speedwiihout some sol1 of gearing or belt reductiorl Think about the problems you would encountertying to run a shaft at I revolution per year accuratelydirectly with a moror If our specificationcalls for a maximum speedof 3600 rpm our encodercat?r?ot have more than 300 countspei rcvolution if we want to maintain the counting time. Using a shorter time will help on the high rym end but will make things harder in the low rpm region, Of coulse, we can also use an encoderwith many fewer counts and have a perf-ectlygood tachometer The soflware we are using employsinteger math, and the largestvariable we can use is a 2-byteword.The largestnumber2 bytescanaccommodaie is 65535-This means that in the COIJNT instruction: couNt PoRTA2, 250, r,t1 The number that ends up in Wl cannot exceed 65535. We can accommodatethis requirementby shotening the 250 millisecond (or less) time frame, but then we will haveproblemswith the 60-rpm endof the specification-The solution is to usethe lowest count that will ser,/eour purposeson the shaft encoderat the lowest speedwe are interestedin. If we use the 20 counts per revolution we discussedearlie! we will be getting (20 * 3600 / 60) = 1200 countsevery secondand a qua er of that every 0.25 seconds or 300 countsevery second,This indicatesthat we could usean elcoder with a few hundred lines per revolution if accurateslow speedirdication was an important consideration. However, adding a higher count encoderto an existing shaft may not be trivial, and adding a f-ew(even 1) equally spacedmarkersonto the shaft manually with a little epoxy or paint may be adequatefor what we need. There is also the possibility that we could write softwarethat would usedifferent rcutines for different speedsof the signal, but for this projecr let's keep it simple. Such sophisticationscanbe addedafter we get proficient at doing the work at hand.The most important thing to keep in mind is that you must understandthe problem in a comprehensiveway before you can createa solution.

DETECTIOI{ Next, we must considerthe componentsand circuitry neededto actually react rdth the signal we are trying to measue (or collect). The simplest way to do this is to react to the changesin the light intensity either as reflected from marke$ on the shaft or as a disturbanceof someother kind in the vicinity. Hall effect sensorsare a popular way of detecting rotation in a dity environment becausethey are rot afected by anything other than magnetic fields. The signal must be convertedto a TTUCMOSlevel signal thatgoeshigh and low reliablywith everychangein the stimulus.Fjgure 15.5shows one way to createsuch an instrument jnterface for the hall effect device. Since the input to the PIC are Schmidt triggers, we would not nomally have to con dition the signal for bounce andjitter

PBO.'ECI r

193

f,FU.qgi!W* From datasheet: Circuits lor Input lrom a Hall eflecl N|LX9021 7.) sensorinlo a PlC,([,{elexis

we will be using the input from a two-channeloptical encoderattachedto a small dc motor as our signal source.This encoderhas 20 slots around its periphery so we will get 20 pulsesper revolution. We will look atjust one channelbecausewe are interested oniy in the signal frequency. The circuitry for the LED pholotransistorpair for the one channelin this delector is as shownin Figure 15.6.

5 VOLTS slgnalisHIGHwhsn thelR LEDis oN and

Circuils for the inpui of a tachometer signalinto a PICfrom the motor optics.

'I94

COUI{III{G PUISE$ A PROGRAIiIABIE TACHOflETER

THE SOFIWARE LeCswrite the code for the LAB-XI first andmake surc we can read the signals,count them,anddisplaythem on the LCD. This letsus build the confidencewe needto proceedto the next level. Then. we will build the tachometeras a stand-alonedevice with the 4 seven segmentdisplays for output. First,as usual,Iet'screatethe codeto enabletheLCD. SeePrc$am I5.1.

tl!,W*S*f{

countingoptlcalencoderpulsesto theLAB-X1

CI,EJAR DEFINE OSC 4 DEFINE LCD_DREGPORTD DEFINE LCD.DBIT ' DEFINE LCD_RSRTG PORTE DEFINE LCD_RSBIT O DEFINE LCD-EREC PORTE DEFINE LCD_EBIT 1 I,OW PORTE.2 aDCONI=%00000111 PAUSE 500

j ; De6ne LCD conneclions ; ; ; ; , ; this nust be set if you are using the IrD ; it mkes the A & E analog ports digital

. -r: TRISC - %00000011 TRISD .%11110000 P O R T D= % 0 0 0 0 0 0 0 0

_ \ 6 - _ - .i a b - e s w a w j I I l s e .

; ; Turns lhe bits

off

AjJPEA VAR WORD RPM VAR WORD ; Then display

lhe

LcD nessage

LCDOIIT SFE, S01, \Tachctrteter PAUSE 250 oop .r,t oisp dys ; -fe , now ready !o be crealed.

!o tell

Reaalyz

us we are ; on lhe frrst 'o-

ready 1ine.

-h- r" hore er i

LOOP! ; the display loop couNt PoREc.o. 250, ArPIra ; read lhe counls into lhe RI,!d=50*a!PIIA*4/5 ; convert counls !o ipn \ ; print ICDOIIT SFE, 9C0, DECII RPM," on line 2 GoIo I.ooP ; do it forever END

Prc

It's that simple with the LAB-Xl and the PBPcompiler Next,let's design the software for the 4 seven-segmentdisplays. Four of them will

allow for a mfiimum displayof 9q99(but sincewe arc takingsamplesfor 0.25seconds,andwe have20countsperrevolution,thema,\imumlpm we canrecognizewithoutreducing thesampling timeis 119,400).

PBOJECit

r95

Max counl:9999in 0.25secords 39.996in I second Thereare20 countsper revolution,which givcs: 1.999.0rcvolutionsper secordr,or (39,996/204"60rcvolutior\sperminute Wc can detect(but no! display)a maxinum of 119,940rpm if we count20 counts If we wantto detectanddisplaya higherrpm,we musl perrcvolutionfor 0.25seconds. the eDcoder count reduccthe time intervalin thc COUNT instructionor dccrease We have alreadyset up PORTD with the lower 4 biN as oumu$ (but if we had not we wouldhave1()addtheline of codeto do thao.After insering an appropriatedecision-naking instruction,we can uscany of thesepiDsfor an output signalto nn apFopriate device. ascovercdin Chapter5, the signalon anyof lf we amplify the signalappropriately, pins can be used to controla heateror punp or whatever mentioDed carlier the output elscwe havein mind.

DISPLAYS SEVEN.SEGMENT displayscomein two types:conlmonanodeandcommoncathodeln Scvcn-segment bolh rypes,onesideof a1lthc LEDSis wired togetherlo makea commonconneclron we will usecommonanode(CA) displaysonly (seeFigure 15 7). In our expenments, l-ED displaysrctually haveeight or nine LEDSin them. Most so-calledseven-segment The eighthandninth LEDSare the decimalpointson one ol two sidesof the number We willnotusethedecimalpoinlsforthis project,so wewill needonly seven displayed. lines,but we will wire in theeighthline ofthe po to activateonedecinal poinl ofeach displayfor possiblefuturcuse. arc used. a litl]e bit abouthow sevensegmentdisplays First.we needto unders[and haveonecommonleg, lhe onc that In a sevensegmentLED display,all the segments on theotherends()1lheLEDs,andwhenthe will goto theanode.The datais impressed gets power, on thesegments to the whalevcrdalais impressed commonlegis connected also all bulthey can areturnedon oneal atime in mostcases, turnedon.The segments pin Often,therewillbe morethanoneanode on adisplay, bc turnedon sinullaneously. bul allofthem will be conncctedtogetherinsidethe display.Theseextn pins areprovided1()makcit easierto lay ou1the wirjng on a printedcircuitboard. in parallelto the data for eachof ihe displaysareconnected All the displayscgnrents is assigned to a scparateline from port, ofthe con lon lines linesto ore PIC andeach is eneryizrd oneat a time modules the PIC on anothefporl. Eachofthe seven-segment so thatit sccmsto the humaneyethat they are all on at the same in rapid succession ljmc. Decidinghow ]ong cach segmentmust be lit and how often the disphy must you comeup with lhc bestdisbc rcfieshedcan be doneon a trial'and-efforbasis1i11 The segnentsarc all the samesizetso they play possibleunderthe circumstances. lesscuffent.It 1nay requircthesamecunent,butthedecimalpointis smallerandnccds be necessary to powerit for a shorterlimc or providea largerrcsistorfor it to malch the brightressolall thc othersegnents.

l !16

TACHOIIIETEB cou flNG PULSES: A PROGMMMABLE

5 VOLTS

220OHMS PHOTO

1 [4EG

display. Flgure 15;7. A commonanodeseven-segment displaywould Oneway oflaliDg oul thecircuitryfor a commonanodefour-chaBcter theeightseg to connect to Wcwould use a conliguouspoft beasshownin Figurc15.8. to be lighted (lbr select the display lhc four unitsin ourcase)!o mentliics anda halfpol1 rinF r. trrir.l=15

THEN

TO@IiE PoRTC . 2 TOGGIJE PORTC.l EIIDTF GCITO UAIN

write check rese! toggle

x to line 2 vaLue of x bhe walue the speaker so re ca

end of testinq

hear it

x

INTCODI.2=0 RESU!dE EAIABIJE

reqd instrucrion, Lo the conpiler interrup! service routine Increnent the counter Clear the interrupt flag Go back to where you were reqd instruction, to the conpiLer

END

aLl

DISASI;E IIiI:[-ROlxTINE

!

programs

nust

end wiLh End

This program toggles line C.2 each time ttfough its cyc]e and gives us a click about oncea second,or onceevery15 internrpts, usinga prcscalar of256. This meansthatthe Llstestinterruptswe could get with Timero would come256 x 15fastet or at about3840 intenupts per secondif we did not changethe clock rate or try to load the timer any other way.The number3480is goodto remernber whenusingTimerobecause it defnesthe empirical m&dmum interupt rate for us. = 3,906.25(thetheoreticalvaluefor a4 MHz processor) r 4,000,000/4/256 = 15.26(used15in thepreceding t 3906.251256 programsincei t is theclosestinteger) | 15+256= 3480(asmentionedearliet not an exactvalue) The prescalarvalue we usehasan impoftanteffect on the lengthofthe intenupt serviceroutine.lf we are using a small value for the prescalar,rhe tine available betweeninterruptsbecomesvery smallandthe monent may comewhenall the time availableis usedup se icing the interruptroutine,leaving no time to do the fore ground task. We will investigatethis by settingthe prescalarwith the first poten tiometeron the LAB-X1 boardand loading its valueinto the prescalarin real time to seewhat happens.To do this, we needthe following code addedto the program. It consistsofreading lhe potentiometerandthenplacingthe rcadvalueinto t]le ibur prescalarbits. The codefor readingPOT I is shownin Program16.2.

2ls

cREAfll|OACCUhAIE I{TEBVAISWttH flitERS! tHE MEInOI|OIES

:liiltiiaii*lgAi

Basicprogram to seetheeflectof theprescalar valueonTimero

AzD V VIR BYTE DEFTNE AlC EtfS I DEFINE .A.DCCLOCK 3 DEFIAIE .A.DCSAITPIJEUS50

; ; j ;

creaLe A2D Value to store resul! set number of bits in resutt sel clock sou.ce (3=rc) set smpling tine in uS

; The value is read with ADCIN O, A2D V _E oisp areo on n- L D t"cDout sFE, DEc3 a2D v $c0. ; The value is then placed OPTION-REG= (A2D ! / 32)

in

o rl

lhe prescalar

-- plo -- wirt

wiLh

When lheselincs of code arc addedto the lrogram the progran becones: Cl'EllR DEFINE OSC 4 DEFINE I,CD DREG PORTD DEFINE IJCD_..DBI!4 DEFIIIE IJCD_RSREGPORTE DEFTNE tCD RSBTT 0 DEFINE LCD EREG FORTE DEFINE LCD EBI! L DEFIIIE .A.DC_BITS8 DEETNE ADC CLOCK 3 DEFINE ADC SAUPI,EUS50 LOw PORTE.2 ; ; ; ; j

with clear ; aluays start speed t defne oscillator ; define LCD connecLions ;4 bit path ; select reg ; selecr brr ; enable reqasler t enable bi! ; set nurber of bits in resul! ) sel clock source {3=rc) i EeL sarpr 19 :me !n L. only ; nake 1ow for write

Seh rhe por! directions, W e n u s t s e t a l l o f P O R T Da n d a l l o f PORTE as ourputs even thoush PoRTE has only 3 1ines. rhe other 5 lines wiLl be iqnored by the systen. D O P I ' i s - e e d e d b e c a - s e . h e p - a z o s p - " k e i. . o r p i r . of _-ispo-l .

IRIsc

= %11111011

TRrsD = 800000000 TRrSE - %00000000 X VtR I{ORD A2D V VAR BYTE .A.DCON1=%00000111

PAUSE 500 LCDOTI! SFE, 1 O!{ IITTERR('PT GOTO I!trI

i ; ; ; ; ; i ; ; ; ; ROIIITNE

".a nora c.2 to speaker conneclion !o output s e L a l l P O R T Dl i n e s t o o u t p u L s e L a l l P O R T El i n e s t o o u l p u ! seL up the wariable create A2D Value to sLore result set Lre Ara,og o D-gi -- .on ro] register needed for the 15F877A see notes pause for LcD to start up clear screen prograr where !o go on ; tel1s ; interrupt (Cohtinued)

flfiERo

2t0

Basicprogramto seethe effeclof the prescalarvalueonTimero iiRiffiHi,{l*l* (Cortnued) operation enable ; sels uP the inierrup! flag so it ; ctears lhe interup!

{:['CON-5-1 IlitTCON. 2 -0

LCDOIXf

SFE,

S80, \!4€trononez;

MAIN:

r.Dcr[I 0, a2D_v OPTION_REG=

(A2D_v

r,cDour sFE. 9c0, GOTO MAIN

waLue for ; sels lhe iniliat 6rst rine display

bit can

x

; the nain loop of the progra ; read channel 0 to A2D_value 1ow nibble | 32) ; set lhe oplion resisrer DEC3 A2D_v/32,n ; display value , do i! asain

fllllcolr.2=0 RSSI'UE ENAB'JE

reqd hslruclion Lo the compiler in!errup! service rouiine logg1e the por! Increnen! lhe counter cLear the interrupt flag go back to where you qere reqd InstrucLion to the conpiler

END

alL

DISASIJE IMT_ROUTINE : TOGGI,E PORTC.2

prosrans

nust

end with

End

In Program I 6.2, the LCD showsus the value of X and the bits that have been set in the OPIION REG register We havehad to removethe comparisonand resettingof the X variablebecauseit takestoo much time andthe toggling hasbeenmovedinto the interrupt se ic€ routine, so you can hearhow often the intenupt is being called. Notice that as the interupts becomemore Aequent,the incrementingof the value of X in the main routinecannotkeepup with the speedwith which the interruptsareaffiving. Eventhough a minimal amountof work is being donein the intenxpt seNiceroutine, it is too much. We can add to the time takenby the interruptserviceroutineby addinga PAUSE in the routine.Playwith addioga PAUSEof between1 and 25 ltsecin the routineto seewhat happens.(Interruptsare missedand the toggling doesnot respondto the changesmade to the option register bits.) Now that we have a feel for the problems involved, lefs lvrite the metronomepro gm.rn.A standardmetronomeprovides between40 and 208 counts per minute. We are going to use POT 0 to control the rate so the 256 values that can be read for the POT mustbe mappedto the 168rates(208 40) neededby the metronome,andeachrate must be accurateenoughto serveeverydaymusical needs, The formula for converting from 0 to 255 to from 40 to 208 is Ticks=40+[(208 40) 'NPOr0]/255 l-ooking back at 3480 asthe maximum numberof jnterruptswe can handlewith ease, and seeingthat we needto genemte168 different hequencies,we se€that we can have about 3480/168= 20 interrupt countssepamtingeachfrcquency,so we know that they canall be differentiated.If we setthe option registerto %0000001I, we will get a prcscalar

22o

cREATING accuBATE|xTEFn LSWITHTIMEhS:IHE lf,EtFOllOltES

This will thenumberoi intenuptsreceivedby a faclorof 16 (256116). of l6 aodincrease job1 means we number of intelTupts by a lactor of 6 Increasingthc be enoughto do the speaker. need!o look at 16times more countson the X counterbefore we loggle the The programfora metronomeusingTinero andtheLAB-Xl is shownin Program 16.3. ,:rPiii0i:iii:ili:3-:l: Workingmetronomebasedon Timeroand the LAB-X1 CIJEAR DEFINE oSC 4 DEFIIIE LCD_DREG PORTD DEFINE LCD_DBIf 4 DEFINE LCD_RSREG PORTE 0 DEFINE LD_RSBlt DEFINE LCD_EREG PORTE DEFIIiIE LCD,EBIT 1 DEFINE aDC_BITS a DEFTNE a.Dc_crJocK 3 DEFTNE a.Dc sAltPl,Eus 50 LOt{ PoRTE.2

; : , :4 ; ; ; ; ; ; i r

sLart with cLear always de6ne oscillaLor speed deine LCD condeclions biL palh SEIECI TEg bit selecL enable TegjisteI bit enable in result set nunrber of bits (l=rc) source ser clock us .6r sa pl:ng e only nake Lov fo! wrile

l " i e n u s t s e t a l l o f p O R T Da n d a l l o f Se! the port directions. PORT'Eas ouLputs e w e n t h o u g h P O R T Eh a s o n L y I 1 i n e s . T h e o t h e i 5 l i n e s r i L L be iqnored by lhe systen. pootc

c 16ad6d

p

6 o -D-ot4

so'p-n2o-i

s oo'

tRISc = %11111011

set PORTC,2to speaker comectron

ERISD - %00000000 ERISE = %00000000 X VAR VIORD PO:TPOSVAR I{ORD A2D 1/ VAR BYTE BDCONl=%00000111

ranes ro ourpuc s e r a L l P O R T EL i n e s t o o u t p u t set up the variabte

PAUSE 500 rcDoua gFE. 1 ON INIIERRUPT GOTO IWE ROUTIIiIE

create A2D Value to store resuLt s e t i h e A n a L o € r! o D i g i t a l control fegister needed for the 16F8?7Asee noLes pause for LCD to start uP Le11s progran

where !o

sets us Lhe inLerrupt enable flag so rt clears the inteuupt

INICON.5=1 INICON.2=0

value

sets Lhe initial MAIIiI: A.DCIN

O,

go on

A2D

ihe nain

loop

prescalar

is

of

V

0 000011 OPTION-REG=%0

16

for

the progran

x

ttMEn0

!&ffffiiwfi*g

227

Worklngmetronome basedonTimenandthe LAB-X1(Continuedl

po4r'os= 208- ( ( (208-40)*a2D_v)/25s)

raDolxt $FE, s80, m€ PorPos," r.cDout $FE, sco, DEc x ," . IF X>=15.15*5o/PO|IPOS EOGCI,E PORI!C.2

THEN

; ; ; ; Lhis is by 15 Coggle

the potentiomeLer position value Display the position display the X count ahere we add the NltipLy the

speaker

x=0 ELSE ENDIF GOIO MAIN

so back and do iL agrain required

DTSAAI.E IITT-ROUTINE: X=X+t INICON.2E0 RESUI'E ENABIJE END

by the

conpiler

increnent walue of x reset/clear the flas

In the wiring diagram shown in Figure 16.3, a ten-pin connectoris shown (for programming the PIC in place) on the ciftuit board.This is an important conv€niencethat should not be omitted on any programmabledevice you cr€ate.You will use it many, many times as you experim€nt with the poject, and not having to take the PIC out of its socketto reprogramit will saveyou a lot of headaches.Take the time to wire in the programmercofirection (in all your Fojects). Next, we need to conveft the program we have developedto run on the tachometer hardware with its seven-segme displays. To allow us to tum the tachometerinto a metronome,we also have to make two hardware additions. We need to add a potentiometer and a speakerto the card. The circuitry for adding thesetwo items is shown circl€din Figure16.3. In order to display on the 4 sevensegmentLED djsplays on the tachometer,we must add the codefor the displays in placeof the instructionsfor the LCD. This codeis taken from the code in the tachometerprogram (with minor modifications as needed)shown in Progran 16.4. Programto usethe tachometerboardas a metronome CI,E'R DEFINE OSC 4 of the nurnbers are lhe inages ; The fotlowing j s t o r e d i _ a e _o r y b e f o l e w a d o o l y r l . n 9 . Tlesd 6--DOFIB ro set .l^e I ro'lc- rn e-ch d-gi.. i b- us-d il di1l require nunbers to suit it. ; Your wirins

wRrrE 1999, %11111111

222

IIIIERVALSWITH TlilEBS:tHE METRONOI{ES CREATING AGCUnATE

Prosramto usethe tachometerboardas a melronome

lltlililiili.iliill6l{lll (Continuedl 9IRITE 2000, WRITE 2001, IIRITE 2002, wRItE 2003. WRITE 2004, wRrTE 2005, vrRIfE 2005, 9IRITE 2007, lrRlTE 2008, l,lRITE 2009,

%00000110 %10111110 %01001100 %00011100 %10110100 %00010101 %00000101 %10011110 %00000100 %00010100

DEFTNE aDC BITS 8 3 DEFINE a.DC_CIJOCR DEFTTIEADc SAMPLEUS50 tRIsA=%o0000000 TRISB-%00000000 TRISC=%11111001 TRISE=%00000100 P VAR WORD X 1IlR BYTE NUII VAR WORD LEDPOS VAR WORD VAI,UE VAI IdORD DIGIT VAR BYTE ADCONl=?00000000 tlitTCON.5=1 INTCON.2=0

oPTroriI_REG-%00000011

, ; ; ; ; ; ; ; ; ;

the the Lhe Lhe the the ihe the the the

nli]rer 0 numltrer 1 nun$er 2 nu!$er 3 mmber 4 nunber 5 nurnber 6 nurnber 7 nlrnlrer I nunber 9

; set ; set ; set

will depend on how your par!icular

in resuLt nunbei of bits clock source (3=rc) sanpling line in us

pause vaiiabte counler wariable number read fron Pot position in display value of metronone counts in dispLay each diqit pause in nicroseconds this selects f,rst line in the table enab}e sets us the inlerrupt ' te npf '1dg so aJ oe _to 16 ; sels Lhe prescalar

; ; ; ; ; ; ; , ;

HIGH DORTC.2

O N I N I E R R U P TG o T o r N T R O U T I N E

6lc p oqrd ; interrupt

rl-r-

o oo o.

MAIN. ; nain Loop of progrran ADCIN 7. liuu ; read channeL 0 pot vaLue ! E D P o s = 2 0 8 - ( ( ( 2 0 a - 4 0 ) * N u M )/ 2 5 5 ) ; the potentiometer ; position value VAIIIE-IJEDPOS ; remenber value we are ; working dlLh is where we add lhe I F X > = 1 6 * 1 5 * 3 0 / L E D P O ST H E N ; t h i s by 16 ; nulriply tOGGtE PORI[C.2 ; toggLe the speaker j reser x x=0 ELSE ENDIF

TIMERO

!gn4!0ll*{e{]: (Continued\

Programto u€ethe tachometerboardas a metronome shor walue on the 4 sewen seer displays do it aqain forewer

GOSUB DISPI,AY GOTO ![AIN DTSPLAY! !!HEN tF vtr-ltE