Programming the PIC microcontroller in c.pdf

ProgrammingthePICMicrocontrollerwithMBasic

AMSTERDAM BOSTON HEIDELBERG LONDONNEW YORK OXFORD PARIS SAN DIEGO

SAN FRANCISCO SINGAPORE SYDNEY TOKYONewnes is an imprint of Elsevier

ProgrammingthePICMicrocontrollerwithMBasic

byJackR.Smith

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v

Contents

Preface............................................................................................................................... xAcknowledgments.......................................................................................................... xiiWhatsontheCD-ROM?................................................................................................ xiii

CHAPTER1:WhatisaPIC?............................................................................................ 1PICs101.................................................................................................................................. 1HowDoITellThemApart?.......................................................................................................... 2WhichOneShouldIUse?............................................................................................................ 4HowDoIPickOne?.................................................................................................................... 7So,WhichOneDoIReallyWanttoUse?..................................................................................... 8BasicMicrosMBasic876Compiler............................................................................................... 8References................................................................................................................................... 9

CHAPTER2:MBasicCompilerandDevelopmentBoards.............................................10TheCompilerPackage............................................................................................................... 10BASICandItsEssentials............................................................................................................. 11DevelopmentBoards................................................................................................................. 13ProgrammingStyle.................................................................................................................... 15BuildingtheCircuitsandStandardAssumptions....................................................................... 16Pins,PortsandInput/Output...................................................................................................... 17Pseudo-CodeandPlanningtheProgram.................................................................................... 23InsidetheCompiler................................................................................................................... 25References................................................................................................................................. 27

CHAPTER3:TheBasicsOutput.................................................................................... 28PinArchitectures....................................................................................................................... 28LEDIndicators........................................................................................................................... 31SwitchingInductiveLoads......................................................................................................... 34LowSideSwitching................................................................................................................... 36IsolatedSwitching..................................................................................................................... 45SpecialPurposeSwitching......................................................................................................... 50FastSwitchingSoundfromaPIC............................................................................................. 50References................................................................................................................................. 51

CHAPTER4:TheBasicsDigitalInput........................................................................... 53Introduction.............................................................................................................................. 53SwitchBounceandSealingCurrent........................................................................................... 58IsolatedSwitching..................................................................................................................... 62

Contents

vi

ReadingaKeypad..................................................................................................................... 63References................................................................................................................................. 66

CHAPTER5:LCDModules............................................................................................... 67SelectingaDisplay..................................................................................................................... 67VFDDisplays.............................................................................................................................. 69ConnectiontoPIC..................................................................................................................... 69HelloWorld............................................................................................................................... 72LCDModuleMemory,ShiftsandLines....................................................................................... 74FontSelection........................................................................................................................... 79CustomCharacters.................................................................................................................... 80References................................................................................................................................. 85

CHAPTER6:ReadingComplexInputSwitches............................................................. 86PinSavingTechniques................................................................................................................ 86RotaryEncoders........................................................................................................................ 91ReadingaRelativeEncoder........................................................................................................ 95DualEncodersandLCD........................................................................................................... 100References............................................................................................................................... 106

CHAPTER7:Seven-SegmentLEDDisplays.................................................................. 107LEDDisplaySelection............................................................................................................... 107CircuitDesign.......................................................................................................................... 108References............................................................................................................................... 119

CHAPTER8:IntroductoryStepperMotors.................................................................. 120StepperMotorBasics............................................................................................................... 120Programs................................................................................................................................. 133References............................................................................................................................... 150

CHAPTER9:RS-232SerialInterface............................................................................. 151HowtoConnecttoYourPC.................................................................................................... 151VoltageLevelsinRS-232andLevelConversion........................................................................ 152StandardPinConnections........................................................................................................ 154AsynchronousTransmission,StartBits,StopBitsandBitOrder................................................. 154MBasicsProceduresforSerialCommunications....................................................................... 156Programs................................................................................................................................. 159References............................................................................................................................... 186

CHAPTER10:InterruptsandTimersinMBasic............................................................ 187InterruptsandTimersOverview............................................................................................. 187Interrupts................................................................................................................................ 188Timers..................................................................................................................................... 194CaptureandCompare............................................................................................................. 203References............................................................................................................................... 210

CHAPTER11:Analog-to-DigitalConversion............................................................... 211IntroductiontoAnalog-to-DigitalConversion........................................................................... 211ResolutionandAccuracy......................................................................................................... 212Self-ContainedDVM............................................................................................................... 218References............................................................................................................................... 230

Contents

vii

CHAPTER12:DigitalTemperatureSensorsandReal-TimeClocks.............................231DS18B20TemperatureSensor.................................................................................................. 231DS1302Real-TimeClock......................................................................................................... 243CombinationDate,TimeandTemperature.............................................................................. 252References............................................................................................................................... 259

CHAPTER13:Assembler101........................................................................................ 260TheBasics............................................................................................................................... 260OpCodes................................................................................................................................. 267References............................................................................................................................... 280

CHAPTER14:In-LineAssembler................................................................................... 281AddingAssemblertoMBasicPrograms.................................................................................... 281Bolt-InAssemblerFunctions..................................................................................................... 295References............................................................................................................................... 316

CHAPTER15:InterruptHandlersandTimersinAssembler.......................................317ISRASMMBasicsGatewaytoAssemblerInterruptServiceRoutines....................................... 317ProgramExamples................................................................................................................... 323References............................................................................................................................... 334

CHAPTER16:Digital-to-AnalogConversion............................................................... 335IntroductiontoDigital-to-AnalogConversion........................................................................... 335ResolutionAccuracyandSignal-to-NoiseRatio...................................................................... 336HenryNyquistandhisSamplingTheorem................................................................................ 337DACCircuitDesign.................................................................................................................. 339AlternativeAnalogOutputSolutions....................................................................................... 352References............................................................................................................................... 358

CHAPTER17:DTMFToneDecodingandTelephoneInterface...................................360WhatisTouch-ToneSignaling?................................................................................................ 360GeneratingTouch-ToneSignals................................................................................................ 361DecodingaTouch-ToneSignal................................................................................................. 361References............................................................................................................................... 388

CHAPTER18:ExternalMemory.................................................................................... 389I2C-BusDevices........................................................................................................................ 389PracticalUseofExternalEEPROM............................................................................................ 403ParallelAccessMemory........................................................................................................... 408References............................................................................................................................... 416

CHAPTER19:AdvancedStepperMotors..................................................................... 418Microstepping......................................................................................................................... 418Programs................................................................................................................................. 420References............................................................................................................................... 452

CHAPTER20:X-10HomeAutomation......................................................................... 453HowX-10Works..................................................................................................................... 453Programs................................................................................................................................. 459References............................................................................................................................... 486

Contents

viii

CHAPTER21:DigitalPotentiometersandControllableFilter....................................487GettingStartedwithanMCP41010........................................................................................ 489RS-232ControlofanMCP41010............................................................................................ 493DaisyChainingMultipleMCP42010Devices............................................................................ 498RS-232CommandofMultipleDaisyChainedMCP42010Devices........................................... 501LogarithmicResponseforAudioVolumeControl..................................................................... 506ElectronicallyTunableLow-PassFilterUsingMCP42010........................................................... 511References............................................................................................................................... 515

CHAPTER22:InfraredRemoteControls...................................................................... 517CommonEncodingStandards................................................................................................. 518IRReceiver............................................................................................................................... 520CharacterizingWide/NarrowPulseIntervals............................................................................. 522DecodingaREC-80Controller................................................................................................. 532References............................................................................................................................... 541

CHAPTER23:ACPowerControl................................................................................... 542IntroductiontoTriacs............................................................................................................... 543SnubberlessversusStandard;dV/dtanddI/dtIssues................................................................. 545TriggeringaTriac.................................................................................................................... 548PhaseandCycleControl.......................................................................................................... 549PowerControlBoard............................................................................................................... 551Programs................................................................................................................................. 555References............................................................................................................................... 565

CHAPTER24:DCMotorControl................................................................................... 567IntroductiontoControlTheory................................................................................................ 567MeasureMotorSpeed(TachometerOutputPulseWidth)......................................................... 568Error=TargetWidthMeasuredWidth................................................................................. 572TheControlAlgorithm............................................................................................................. 572MotorControlPrograms.......................................................................................................... 573References............................................................................................................................... 594

CHAPTER25:BarCodeReader..................................................................................... 595BarCodes101.................................................................................................................... 595BarCodeWand....................................................................................................................... 599Programs................................................................................................................................. 602References............................................................................................................................... 631

CHAPTER26:SendingMorseCode.............................................................................. 633MorseCode101..................................................................................................................... 633Programs................................................................................................................................. 635References............................................................................................................................... 660

CHAPTER27:MorseCodeReader................................................................................ 661SendingandReceivingMorse.................................................................................................. 661ToneDetectorCircuit............................................................................................................... 663Programs................................................................................................................................. 668References............................................................................................................................... 689

Contents

ix

CHAPTER28:WeatherStationandDataLogger........................................................691SensorSelection...................................................................................................................... 691ConnectingtheSensorsandMemory...................................................................................... 698InitialTests............................................................................................................................... 700References............................................................................................................................... 728

CHAPTER29:Migratingfromv5.2.1.xto5.3.0.0andtheUndocumentedMBasic.....729Migratingfromv5.2.1.xto5.3.0.0.......................................................................................... 729UndocumentedMBasic........................................................................................................... 733

APPENDIXA:PartsListandSuppliers.......................................................................... 745Suppliers................................................................................................................................. 745GenericComponentsRequired................................................................................................ 746SpecificComponents............................................................................................................... 748

APPENDIXB:FunctionIndex........................................................................................ 755

AbouttheAuthor......................................................................................................... 760Index.............................................................................................................................. 761

x

Preface

MyintroductiontocomputerswasinthedaysofIBMsModel29cardpunch.YoufirstcarefullyprintedyourFORTRANcodeonacodingsheet,thenpunchedacarddeckandfinallywalkedyourcardsovertothecampuscomputercenter.There,oneofthehighacolytesoftheIBM360inrealityagradstudentac-ceptedthedeckwithafaintlookofdisdain.Youmightevencatchaglimpseofthecomputeritselfthroughtheglasswallofthecomputercenter.Thefollowingday,ifyouwerefortunate,yourcarddeckwasreadyforpick-up,wrappedinthegreenbarpaperoutputyourjobelicited.Ifyouwerereallylucky,theoutputmadesenseandyoucouldgoontoyournexttask.Ifyouwerelessfortunate,theprintoutidentifiedyourerrors.And,ifyouwerereallyhavingabadday,yourcarddeckwashiddeninsideaninch-thickcoredumpprint-out,densewithhexadecimalregisterandmemoryvalues.

Today,wehaveasmuchcomputingpoweronourdesktopsaswasbehindtheglasswallwhenIwaspunch-ingcarddecks.Computersarenowembeddedinalmosteveryimaginableelectronicdevice.OneofthepioneersinembeddedcomputerswasGeneralInstruments,whichin1976releasedthe1650programmableintelligentcomputer,thegrandfatheroftodaysPICs.(ThereisaragingdebateamongthecognoscentioverthetruenamebehindthePICacronym,withperipheralinterfacecontrolleroftenbeingcited.GIs1977datasheetforthePIC1650,though,confirmsthetermprogrammableintelligentcomputer.MicrochipTechnologyIncorporated,whoacquiredGIsPICbusinessinthemid1980s,wiselystaysoutofthedebateandjustcallsitsproductsPICmicromicrocontrollers.)

ThisbookfocusesonprogrammingMicrochipsmid-rangePIClinewithMBasic,apowerful,buteasytolearnprogramminglanguage,developedbyBasicMicroofMurrieta,California.SinceaPICbyitselfisnotallthatuseful,IwillillustrateMBasicsabilitiesthroughaseriesofconstructionprojects,somesimpleandsomemoreadvanced.Iwillalsodipintoassemblerlanguage,astherearesomeapplicationsthatrequireustobecomemoreintimatewiththePICsinternalsthanpossibleinMBasic.

TheprojectsassumetheuserhasMBasicProfessionalversion5.3.0.0compiler,theassociatedISP-PROprogrammeranda2840developmentboard,allavailablefromBasicMicro.Almostallexamplesusea16F877APICanda20MHzresonator.However,boththecodeandsupportingcircuitryareeasilyportabletomanyotherPICssupportedbyMBasic.Moreimportantly,almosteveryprojectinthisbookcanbebuiltwiththefreeMBasic876compilerincludedintheaccompanyingCD-ROM.Inafewcases,the16F876doesnthaveenoughI/Opinstosupporttheproject.

ReadingBasicMicrosmessageboard,andquestionsfrombeginnerspostedtothePICmicrocontrollerdiscussionlist,revealsaneedforinformationshowinghowthesmorgasbordoffunctions,proceduresandcodesnippetsfoundintheMBasicUsersGuidemightbeputtogethertoactuallydosomethinguseful.And,sincedoingsomethingusefulwithaPICinevitablyrequiressomeassociatedcircuitry,electronicsques-tionsaresprinkledliberallythroughouttheseforaaswell.

Preface

xi

IvetriedtoaddressboththesoftwareandhardwareaspectsofworkingwithPICs,withmyimaginedreaderhavinganinterestinbothprogrammingandelectronics,butwithoutspecializedtraining.AlthoughIvetriedtoerronthesideofinclusionoverbrevity,thisbookcantreplaceabasicunderstandingofelectronics,noranelementarygraspofhowonegoesaboutwritingBASICprograms.Itrustthatreadersexperiencedinelectronicswillforgivethesimplificationsnecessitatedinthisendeavor,andthatexperiencedprogrammersunderstandthattheywillnotnecessarilyfindelegantalgorithmsorcodeineverycase.But,thisworkisnotintendedtoreplicateKnuthsTheArtofComputerProgramming,norHorowitzandHillsTheArtofElec-tronics.And,IcouldntduplicateeitherifItriedmybestforthenextdecade.

Finally,Iveneverfoundtheimpersonalpassivetechnicalwritingstyleconducivetolearninganewsubject.Afterall,thecodewastransferredtothePICisntwhatactuallyhappenedwasit?Someoneprobablyyou,butcertainlynotsomedisembodiedentityprogrammedthePICusingtheMBasicsoftware.Whynotsayso?Likewise,althoughweknowthataPICsoutputpindoesntseealoadresistancethroughphysicaleyes,theseanthropomorphicanalogiesareeasiertounderstandthanreadingtheequivalentresistancethatwouldbemeasuredbyanappropriateimpedancemeasuringinstrumentconnectedinplaceofthepinandapplyinga+5voltdcstimulussignaltotheloadresistance.Hence,Imakenoapologiesforthechattystyle.

ThisbookisnotanofficialpublicationofBasicMicro,anditscontentsreflectmyviews,notthoseofBasicMicro,oritsemployeesorowners.

Inabookofthislengthanddetail,therewillinevitablybeerrorsandomissions,despitethebesteffortsoftheauthorandeditors.Somearetheunavoidablebyproductofsimplifyingcomplexsubjectsforanintro-ductorylevelpresentationandothersarejustplaindumbmistakes.Regardlessofthecategory,Iacceptfullresponsibility.Imaybecontactedbye-mailatJack.Smith@cox.nettoreporterrorsoromissions.

JackSmith

June2005,Clifton,VA

xii

Acknowledgments

AcknowledgmentsareduetomywifeJanet,whohastoleratedwithgoodgracetheinnumerablehoursIvespentinthebasementworkshoporinfrontofthecomputerscreen.IalsowishtothankthepeopleatBasicMicro,includingNathanScherdin,andDaleKubin,fortheirassistanceinwritingthisbook.IalsowishtothankLarryandJanetPhippsforthehospitalityshowntome.

xiii

WhatsontheCD-ROM?

ThecontentoftheCD-ROMwasdevelopedwithWindowsXP,andhasbeenverifiedasreadablewithWindows2000.Ithasnotbeentestedwithotheroperatingsystems.

Itscontentsareorganizedinaseriesofdirectories:

MBasic876

BasicMicroInc.hasprovidedafreeMBasiccompiler,MBasic876,withallfeaturesofMBasicProfession-al,butrestrictedtoprogramonly16F876and16F876Adevices.Aninstallationprogram,MBasic876_Setup,toaddMBasic876toyourcomputeriscontainedinthisdirectory.LaunchingMBasic876_Setupwillstarttheinstallationprocess.

ThedirectoryMBasic\DocumentscontainstheMBasicUsersGuideanddatasheetsonBasicMicrosprogrammingboardanddevelopmentandprototypeboards.

BasicMicroswebsite,http://www.basicmicro.com/,hasanactiveMBasicusersforumthatIhighlyrecommend.

LinearTechnologyCircuitSimulationSoftware

LinearTechnologyCorporationhasprovidedtwoprogramsforcircuitsimulation.Bothprogramswereusedindevelopingandillustratingthecircuitsinthisbook.

ThedirectoryLinearTechnologyCircuitSimulationSoftware\FilterCADcontainstheinstallationprogram,FilterCADv300.exe,whichinstallsFilterCADversion3.00onyourcomputer.FilterCADisapowerfultoolfordesigningandsimulationactivefilters.

ThedirectoryLinearTechnologyCircuitSimulationSoftware\SWCADIIIcontainstheinstallationprogramswcadiii.exe,whichinstallsaprogramcalledLTspice/SwitcherCADIIIonyourcomputer.Thisisafull-fea-turedgeneral-purposeelectroniccircuitsimulationprogram.AfterinstallingLTspice,Irecommendyouusetheautomaticupdatefeaturetodownloadthemostrecentversion.

YoumayalsowishtojointheLTspiceusersgroup,viathehomepageathttp://groups.yahoo.com/group/LTspice/.

MBasicPrograms

Alloftheprogramsinthisbookarecontainedinthisdirectory.Theprogramsareorganizedwithaseparatedirectoryforeachchapter.WithineachchapterdirectoryareseparatedirectorieswithprogramversionscompatiblewithMBasic(andMBasic876)version5.3.0.0andwithearlierversions(5.2.1.1.)Idevelopedtheprogramswithversion5.2.1.1originally,buthaverevisedandtestedeachforcompatibilitywithversion5.3.0.0.

xiv

DataSheetsandApplicationNotes

Datasheetsformanyofthetransistors,diodesandintegratedcircuitsusedinthisbookscircuitsarepro-videdinthedirectorydatasheetsandapplicationnotes.Inaddition,Ihaveincludedaselectionofrelevantapplicationnotesandothermaterialfromkeysemiconductormanufacturers.

Eachmanufacturersdatasheetsarecontainedinadirectorynamedafterthemanufacturer.

WhatsontheCD-ROM?

1

CHAPTER 1PICs101

WhatisaPIC?PICsareinexpensiveone-chipcomputersdesignedandmanufacturedbyMicrochipTechnology,Inc.TheacronymoriginallystoodforProgrammableIntelligentComputer,butMicrochipsofficialnameforthesedevicesisnowPICmicromicrocontrollers.WewillcallthemPICs.In1977,GeneralInstruments,Microchipspredecessor,developedtheoriginalPIC,thePIC1650.ThePIC1650canbethoughofasthegrandfatheroftodaysPICs,anditsarchitecture,programmingapproachandotherfeaturesdirectlycorre-spondtothosefoundinmodernPICs.ItsinstructionsetandregisterarrangementmirrorcurrentPICswithonlyminordifferences.

GeneralInstrumentssolditsmicrocontrollerbusinessinthemid-1980stotheentitythatlaterbecameMicrochip.Microchipscurrentproductlineincludesnearly200PICmodelswithMBasicsupportingmorethanhalf.Microchiphassoldmorethan2billionPICssincethemid-1980s,andin2002wasnumberoneworldwidein8-bitmicrocontrollersales,basedonnumberofunitsshipped.

PICsaremicroprocessors,akintotheonesinsidepersonalcomputers,butsignificantlysimpler,smallerandcheaper,optimizedtodealwiththerealworldoperatingrelays,turninglampsoffandon,measuringsensorsandrespondingtochangedreadingswithspecificactionsinsteadofrunningwordprocessingorspreadsheetprograms.Toemphasizetheoutsideworldconnection,thetermmicrocontrollerwascoinedtodistinguishitfromamicroprocessors.GIenvisioneditsPIC1650asameanstoreplacedozensofdiscretelogicchipsincomputersusingitsCP1600microprocessor,butimmediatelyrecognizedthepowerofitsflexible,programmabledesignservingasastand-alonemicrocontroller.Figure1-1illustratesthemainelementsinsideaPIC:

Aprocessingengine:Thecentralprocessingunit,orCPU,isthemicrocontrollersintelligence.ItperformsthelogicalandarithmeticfunctionsofthePICfollow-inginstructionsitreadsfromtheprogrammemory.Itreadsfromandwritestodatamemoryandtheinput/outputmodule.

Programmemory:HoldsinstructionsfortheCPU.TheCPUreadsprogrammemorybutisphysicallypreventedinmostmodelPICsfromwritingtoprogrammemory.

Datamemory:Holdsmemorythattheprogrammermayuseforvariables.TheCPUreadsfromandwritestodatamemory.

Input/output:HowthePICcommunicateswiththeworldoutsidethechip;forexample,pinsthatgobe-tweenlogical0andlogical1. Figure1-1:MainelementsofaPIC.

Chapter1

2

Peripherals:SpecialpurposefunctionsbuiltintothePIC,suchastimers,analog-to-digitalconvertersandpulsewidthmodulators.

IfyouarefamiliarwiththeIntelmicroprocessorsusedinIBM-compatiblepersonalcomputers,youmayno-ticeonestrikingdifferenceinFigure1-1;theprogrammemoryanddatamemoryareseparate.Incomputertechno-speak,PICsfollowtheHarvardarchitecturemodel,whileIntelsmicroprocessors(andthoseofmostothermanufacturersaswell)implementvonNeumannsarchitecture,sharingcommonmemorybetweenprogramanddataasnecessary.Fortunately,MBasichidesthedetailsofthisdifferencefromusandweseldomneedtodelveintoit.Oneplacethisdifferenceiscritical,though,issincedatamemoryandprogrammemorycapacitiesareseparatelyspecifiedinPICs,bothmustbesizedtoaccommodatethejobathand.

HowDoITellThemApart?MicrochipidentifiesPICswithamultipartidentifiersuchasa16F877A-E/P:

MicrochipgroupsitsPIClineinthreeperformanceandthreememorytypecategories:

MicrochipsGeneralPurposePICLineName(InstructionWordLength)andMBasicSupport

ProgramMemoryType Base-Line(12-bit) Mid-Range(14-bit) High-End(16-bit)

EPROM/EEPROM

NonesupportedbyMBasic

12C,12CE,16Cand16CE-seriesEPROMandEEPROM

17C-seriesand18C-series.NotsupportedbyMBasic

Read-onlyMemory(ROM)16CR-series.Notsupported

byMBasicNotproducedby

Microchip

Flash(electronicallyerasable)Some12F-seriesand

16F-series

18F-series.NotpresentlysupportedbyMBasic

(SeeNote1)1.18F-seriessupportisunderdevelopmentbyBasicMicroandwillbeincludedinafutureMBasicrelease.

ItwouldhavebeenlogicalforMicrochiptousetheseriesidentifiertopointtotheinstructionwordlength,butitmissedthatopportunity.Thus,wehavethe12C508A,a12-bitdeviceandthe12F629,a14-bitdevice.And,wehavethe16C54C,a12-bitdeviceandthe16C554,a14-bitdevice.Inalmostallbutunfortunatelynotentirelyallinstancesa16-seriesdeviceisamid-rangePICwitha14-bitinstructionword,buttobesurewemustconsultMicrochipsreferencedocuments.

16 F 877 A -xx E /P

Case style P,JW, SO,SP,ML,SS,PT

Temperature range, E (extended), I(industrial) or C (commercial)

Maximum clock frequency in MHz(omitted if only one frequency ratingapplies for the PIC.)

Silicon die layout revision suffix

Device type number

Program memory type; C, CR, CE & F

Family number; 12, 16, 17 & 18

PICs101

3

Theinstructionwordlengthisnotrelatedtotheprogrammemorysize,butratherdefineshowmanyuniquemachinecodeinstructionsmaybeimplemented.ItisntnecessarytogointodetailsasMBasictakescareofthisforus,butmanymachineleveloperandsincludean8-bitliteralvalue,suchasmovingadefinedbytevalue(theliteral)intotheCPU.Sincethe8-bitliteralispartoftheinstruction,a12-bitinstructionwordleavesonlyfourbitsforinstructionscontainingaliteral,resultinginonly16possibleuniqueinstructions.Movingtoa14-bitwordincreasesthepotentialinstructionsetwithaliteralto64.(Theproblemoflimitedprograminstructionwidthalsoshowsupinassemblerjumporgotoinstructions.)Inanyevent,sinceMBasiccurrentlysupportsonlymidlength(14-bit)PICs,wecanfilethisinformationintheinterestingbutnotimmediatelyusefulcategoryinthebackofourminds,atleastuntilwestarttomixassemblerlanguageroutineswithMBasic.

ProgrammemoryinaPICmayconsistofthreetypes:

Read-only:Read-onlymemorymeansexactlythat;thememoryisconfiguredatthetimeofmanufactur-ingtocontaintheprogramcodeandmaynotbesubsequentlyaltered,somethingeconomicallyfeasibleonlyinhighvolumeproducts.MBasicdoesnotsupportPICswithread-onlymemory.

EPROMandEEPROM:EPROM(erasableprogrammableread-onlymemory)andEEPROM(electri-callyerasableprogrammableread-onlymemory)memorymaybewrittentoelectronicallythroughtheapplicationofaprogrammingvoltagetothePIC.Oncewritten,EPROMmemorymaynotbere-written,andisthusbecomesread-onlyafterwards.Microchipreferstothesedevicesasonetimeprogram-mableorOTPproducts.EEPROMdevices,however,maybeerasedthroughseveralminutesexposuretoultravioletlight.Electrically,MicrochipsEPROMandEEPROMchipsusethesametechnology,withEPROMchipsbeingencapsulatedinopaqueepoxy.EEPROMchipshaveaquartzwindowthroughwhichUVlightmayreachthechipsurface.(Afterprogramming,youcoverthewindowwithanopaquelabeltopreventerasurethroughambientsunlightorfluorescentlightexposure.)EPROMPICsmaybeusefulinsmalltomediumvolumeproduction,butbothEPROMandEEPROMdevicesarerapidlybe-ingsupplantedbyflashmemoryPICs.

Flash:Flashmemorymaybewrittentoanderasedelectronicallythroughtheapplicationofaprogram-mingvoltagetothePIC.Flashmemorymaybewrittentohundredsofthousandsoftimeswithouterrorand,atroomtemperature,basedonextrapolatedlifetesting,willretaindatafor100years.FlashisidealfordevelopingprogramsandlearningMBasic,asrevisingcodeandwritingtherevisedprogramtoflashrequireswellunderaminuteforallbutthelongestprograms.

LookingatthepriceofchipsofsimilarperformanceandcapacitywithEPROM,EEPROMandflashmemorytypes,itseasytoseewhyflashdevicesaretakinganincreasingshareofthemarket.

MemoryType PartNumber Packaging UnitCost

EEPROM(UVerasable) 16CE625/JW Ceramicwindowed18-pinDIP(CDIP)TypeJW $10.64

EPROM(one-timeprogramming) 16CE625/P Plastic18-pinDIP(PDIP)TypeP $4.38

Flash 16F628A Plastic18-pinDIP(PDIP)TypeP $3.05

Finally,withineachcategory,Microchipoffersstandardvoltage(5voltnominal)andextendedvoltage(minimumvoltagedependentuponmemorytype;compatiblewith5voltsupply;somewithbuilt-inregula-torforoperationfromhighervoltages.)PICsalsohaveawidevarietyofmemorysize,internalperipheraloptions,temperatureranges,maximumoperatingfrequencyandpackaging.Thesevariantsareidentifiedthroughassociatedalphanumericdesignators.

Chapter1

4

MemoryandVoltageDesignators

Memory/VoltageLetter

Memory/VoltageType

C EPROM

CR ROM

CEOne-timeprogrammable(EPROM)and

EEPROM(erasable)

F Flash

HV HighVoltage(15V)

LF LowVoltageFlash

LC LowVoltageOne-timeprogrammable

LCR LowVoltageROM

TemperatureRangeDesignators

TemperatureLetter

TemperatureRange

C Commercial0Cto+85C

I Industrial-40Cto+85C

E Extended-40Cto+125C

PartialListofPackageDesignators

PackageOptionLetter Package

JW Ceramicwindow(EEPROMonly)

P PlasticDIPSP/PJfor28pinx0.3(skinny-dip)

SN,OA,SM,SL,OD,SO,SI SOIC-plasticsmalloutline;surfacemount

PQ QFP-Plasticquadflatpacksurfacemount

SS SSOP-plasticshrinksmalloutlinesurfacemount

ML Chipscalepackage

ST TSSOP-Plasticthinshrinksmalloutlinesurfacemount

PT TQFP-plasticthinquadflatpack

WhichOneShouldIUse?LetslookatthePICssupportedbyMBasic.

PICSSupportedbyMBasic

DeviceDataRAM ADC

ProgramMemory SerialI/O Speed Timers

LowVoltageDevice

PIC12CE673 128 4 1024 10 1+WDT PIC12LCE673

PIC12CE674 128 4 2048 10 1+WDT PIC12LCE674

PIC12F629 64 - 1024 20 2+WDT PIC12F629

PIC12F675 64 4 1024 20 2+WDT PIC12F675

PIC16C554 80 - 512 20 1+WDT PIC16LC554

(continued)

PICs101

5


DeviceDataRAM ADC


LowVoltageDevice

PIC16C558 128 2048 20 1+WDT PIC16LC558

PIC16C620 80 512 20 1+WDT PIC16LC620

PIC16C620A 96 512 40 1+WDT PIC16LC620A

PIC16C621 80 1024 20 1+WDT PIC16LC621

PIC16C621A 96 1024 40 1+WDT PIC16LC621A

PIC16C622 128 2048 20 1+WDT PIC16C622

PIC16C622A 128 2048 40 1+WDT PIC16LC622A

PIC16C62A 128 2048 IC,SPI 20 3+WDT PIC16LC62A

PIC16C62B 128 2048 IC,SPI 20 3+WDT PIC16LC62B

PIC16C63 192 4096 USART,IC,SPI 20 3+WDT PIC16LC63

PIC16C63A 192 4096 USART,IC,SPI 20 3+WDT PIC16LC63A

PIC16C642 176 4096 20 1+WDT PIC16LC642

PIC16C64A 128 2048 IC,SPI 20 3+WDT PIC16LC64A

PIC16C65A 192 4096 USART,IC,SPI 20 3+WDT PIC16LC65A

PIC16C65B 192 4096 USART,IC,SPI 20 3+WDT PIC16LC65B


PIC16C662 176 4096 20 1+WDT PIC16LC662


PIC16C71 36 4 1024 20 1+WDT PIC16LC71

PIC16C710 36 4 512 20 1+WDT PIC16LC710

PIC16C711 68 4 1024 20 1+WDT PIC16LC711

PIC16C712 128 4 1024 20 3+WDT PIC16LC712

PIC16C715 128 4 2048 20 1+WDT PIC16LC715

PIC16C716 128 4 2048 20 3+WDT PIC16LC716

PIC16C717 256 6 2048 IC,SPI 20 3+WDT PIC16LC717


PIC16C72A 128 5 2048 IC,SPI 20 3+WDT PIC16LC72A

PIC16C73A 192 5 4096 USART,IC,SPI 20 3+WDT PIC16LC73A

PIC16C73B 192 5 4096 USART,IC,SPI 20 3+WDT PIC16LC73B

PIC16C745 256 5 8192 USB,USART 24 3+WDT

PIC16C74A 192 8 4096 USART,IC,SPI 20 3+WDT PIC16LC74A

PIC16C74B 192 8 4096 USART,IC,SPI 20 3+WDT PIC16LC74B

PIC16C76 368 5 8192 USART,IC,SPI 20 3+WDT PIC16LC76

PIC16C765 256 8 8192 USB,USART 24 3+WDT






PIC16C923 176 4096 IC,SPI 8 3+WDT PIC16LC923


PIC16CE623 96 512 30 1+WDT PIC16LCE623

PIC16CE624 96 1024 30 1+WDT PIC16LCE624

PIC16CE625 128 2048 30 1+WDT PIC16LCE625(continued)

Chapter1

6


DeviceDataRAM ADC


LowVoltageDevice

PIC16F627 224 1024 USART 20 3+WDT PIC16LF627

PIC16F628 224 2048 USART 20 3+WDT PIC16LF628

PIC16F73 192 5 4096 IC,SPI,USART 20 3+WDT PIC16LF73



PIC16F83 36 512 10 1+WDT PIC16LF83

PIC16F84 68 1024 10 1+WDT PIC16LF84

PIC16F84A 68 1024 20 1+WDT PIC16LF84A

PIC16F870 128 5 2048 USART 20 3+WDT PIC16LF870

PIC16F871 128 8 2048 USART 20 3+WDT PIC16LF871

PIC16F872 128 5 2048 IC,SPI 20 3+WDT PIC16LF872

PIC16F873 192 5 4096 USART,IC,SPI 20 3+WDT PIC16LF873

PIC16F873A 192 5 4096 USART,IC,SPI 20 3+WDT PIC16LF873A







Thislistmayseembewilderingatfirst,soletsgothroughthetablesparameters:

DeviceThisissimplyashortformofthedevicepartnumber.DataRAMDataRAMspecifiestheamount(inbytes)ofrandomaccessmemoryavailabletoholdvari-

ablesinyourMBasicprogram.SinceMBasicrequiressomeRAMforitsinternalusenotalltheDataRAMwillbeavailableforyourprograms.RAMcontentsarelostwheneverthepowerisremovedfromthePIC.(ManydevicesincludenonvolatileEEPROMmemoryaswell.WelluseEEPROMmemoryinseveralsampleprogramsinlaterchapters.)

ProgramMemorySincePICsareHarvardarchitecturedevices,theprogramanddatamemoryareseparate.TheProgramMemorycolumn,followingMicrochipsdocumentation,identifiestheprogrammemorysizeinprogramwords.InthecaseofthePICssupportedbyMBasic,thewordlengthis14bits.TheMBasiccompiler,however,reportsprogrammemoryusein8-bitbytes,asshowninFigure1-2.Shouldyouwishtoconvertbetweenthetwo,thecompilerreportsone14-bitwordas1.75bytes,andconversely,1byterepresents0.5714314-bitwords.

ADCAnanalog-to-digitalconverter(ADC)allowsthePICtoreadthevalueofananalogvoltageandconvertittoanumeri-calvalue.Dependinguponthemodel,theADCmayhave8-bit,10-bitor12-bitresolution.Chapter11showshowtousetheADCtobuildadigitalvoltmeter.

Figure1-2:UnderstandingMBasicsmemoryusagereport.

PICs101

7

SerialI/OCertainPICshavespecializedhardwaresupportofuptothreeserialstandardprotocols:TheUSART(universalsynchronousasynchronousreceivertransmitter)supportsthecommonRS-232-typeasynchronousprotocol,aswellasothers;IC(inter-integratedcircuit)andSPI(serialperipheralinterface)arebothprimarilyusedtocommunicatebetweenthePICandotherintegratedcircuits,suchasadd-onmemory,temperaturesensors,serialnumbergeneratorsandthelike.MBasichowever,imple-mentsRS-232-typeserialcommunications(theSerInandSerOutprocedures),aswellasI2C(theI2CinandI2Coutprocedures)andSPI(viatheShiftInandShiftOutprocedures)insoftware,soallthreeprotocolsareavailablewhetherornotthePIChastheassociatedspecializedhardware.Indeed,insomerespectsMBasicssoftwaresolutionissuperior,asitpermitsuser-definedpinassign-ments,whileMicrochipshardwareimplementationistiedtospecificpins.However,MBasicsupports,throughtheHserOutandHSerInprocedures,certainaspectsoftheUSARThardwareforthosePICssoequipped.Wellseehowthisworksinlaterchapters.

SpeedThemaximumclockspeedinMHzthatthePICdevicetypesupports.Microchipproduceslowerthanmaximumspeedversionsofsomedevices,however,sowhenpurchasingaPICcheckthespeedsuffix.DontbuyaPIC16F876-04/SP(4MHzmaximum)ifyouwantaPIC16F876-10/SP(10MHz)oraPIC16F876-20/SP(20MHz)product!Thepricedifferencebetweentheslowerspeedversionofadevicetypeandthemaximumspeedversionisusuallymodest.

TimersTimersareprogrammableinternalcounters.AmongtheirmanyusesistosetupaperiodicinterruptsignalthatcausesthePICtoperformthecodeattheinterrupthandler.Thewatchdogtimer(WDT)isaspecializedtimerthatmaybeusedtodetectandtakeactionuponthemainsoftwarefreezing.TimersandinterruptsarethesubjectofChapter10.

LowVoltageDeviceHistorically,PICshaverequireda5-voltpowersupply,orVDDvoltage.Withthetrendtowardslowervoltagelogic,MicrochiphasrespondedwithlowvoltagealternativesofitsstandardPIClineup.ThelowvoltagechipsareidentifiedwithanLinthesuffix,andoperatewithaslittleas2.0VVDD,althoughslowerspeedmaybenecessaryatthelowerendoftheoperatingvoltagerange.Fortu-nately,MicrochipslowvoltagePICsalsofunctionwiththetraditional5VsupplysotheymaybeusedwithBasicMicrosICPanddevelopmentboards.

HowDoIPickOne?Thefirststepistoidentifyyourrequirementsandthenfindthematchingdevices.

HowmanyI/Opinsdoyouneed? HowmuchRAMisrequired?EachbytevariabledeclaredinMBasicconsumesonebyteofRAM,each

wordvariabletwobytesandeachlong,fourbytes. Howmuchprogrammemoryisrequired?AsacrudeestimateoftheMBasicprogramsizethatfitsintoa

particularprogrammemorycapacity,youmayassume4001300wordsforlibraryfunctionsand820wordsperlineofexecutablecode,dependinguponthecompileroptimizationchoice(minimumsizeormaximumspeed),themixofinstructionsusedandthelengthoftheprogram.Themoredifferentproce-duresandfunctionsused,thelargerthelibraryrequirement.

Howfastadevicemeetsyourspeedrequirements? Doyouneedspecialpurposefunctions,suchasanA/Dconverter,aUSART,specifictimersoraninter-

nalclockoscillator? Howdoesthecostfitintotheprojectbudget? Doyouwantaone-time-programmableoraflashmemorydevice? Aretherephysicalpackagepreferences? Islow-voltageoperationnecessary?

Chapter1

8

Ifyourrequirementsareuncertain,startwiththelargest,mostfullyequippedPICavailable,andrefineyourdeviceselectionlaterasyouarefurtheralongtheprocess.MBasicmakesthisprocessespeciallyeasy,asthesameMBasiccoderunsonanysupportedPIC,except,ofcourse,forahandfulofinstructionsdependentuponparticularhardwarefeatures.

So,WhichOneDoIReallyWanttoUse?WhileyourchoiceofPICmaybecriticalifyouareplanningaproductionrunof100,000products,forgeneralexperimentationandeducation,Ipreferthe16F876and16F877devices,eithertheoriginalorthe876A/877Aversions.(Formostpurposes,thereisntasignificantdifferencebetweentheoriginalandAsuffixed876and877PICs.)OfthechipscurrentlyusablewithMBasic,thesefourdevicesofferthemaximumavailableprogrammemory(8192words),themaximumRAM(368bytes)andhavetheotherbellsandwhistlesofferedbyMicrochip,suchasaUSARTandanA/Dconverter.Foraparticularproject,thechoicebetweenthetwoisdrivenbythenumberofinput/outputpinsrequired,withthe876chipshavingamaximumof22possibleI/Opins,whilethe877chipsincreaseto33possibleI/Opins.And,ofcourse,theseareflashmemorydevicessoweneednotworryaboutUVerasers.

Forsmallerprojects,the16F628isworthyofconsideration.Itisavailableinan18-pinpackage,soitmustbeusedwithBasicMicros0818developmentboard.The628hasamaximumI/Ocapacityof16pins,andhasgenerous224bytesRAMand2048wordsofprogrammemory.ItdoesnothaveanADC.

Finally,forjobsthatrequireatinyPIC,the12F629and12F675devicesareuseful.Bothhaveasmallfootprint(8-pinDIPpackage),1024wordsofprogrammemoryand64bytesofRAM.The12F629doesnothaveanA/Dconverter,whilethe12F675does.BothpermituptosixoftheireightpinstobeusedforI/Opurposes.EitherchipmaybeusedwithBasicMicros0818developmentboard.

BasicMicrosMBasic876CompilerTheCD-ROMaccompanyingthisbookincludesafreeMBasic876compilerfromBasicMicro.MBa-sic876isacomplete,100%functionalversionofMBasic,limitedinthatitworksonlywiththe16F876and16F876Adevices.TouseMBasic876asintended,withintegrateddebuggingandinteractiveprogramming,youwillneedtopurchaseBasicMicrosin-circuitprogrammer(ISP-PRO)andits2840DevelopmentBoard.Or,ifyouarewillingtosacrificeintegrateddebuggingandinteractiveprogrammingbothfeaturesofgreatbenefityoumayuseMBasic876soutputHEXcodewiththird-partyPICprogrammers.WelllookattheISP-PROand2840DevelopmentBoardinChapter2.

YoushouldnotregardMBasic876srestrictiontothe876and876Adevicesasaseriouslimit,asthesechipsarefeatureandperformancerichand,infact,arethemostadvancedmid-rangePICsavailableina28-pinpackage.WithonlyahandfulofexceptionswheremoreI/Opinsarerequiredthanareavailableina28-pinpackageeverycircuitinthisbookcanbeconstructedwithan876/876A,andtheassociatedprogramscompiledbyMBasic876.

PICs101

9

References[1-1]MicrochipprovidesawealthofPICinformation,availableforfreedownloading,onitsInternetwebsite,

http://www.microchip.com.Allareworthreading,butofparticularinteresttobeginnersaretheintro-ductorytutorialsfoundathttp://www.microchip.com/1010/suppdoc/design/toots/index.htmincluding:

Analog-to-digitalconversion:http://www.microchip.com/download/lit/suppdoc/toots/adc.pdf Deviceconfiguration:http://www.microchip.com/download/lit/suppdoc/toots/config.pdf Powerconsiderations:http://www.microchip.com/download/lit/suppdoc/toots/power.pdf On-chipMemory:http://www.microchip.com/download/lit/suppdoc/toots/ramrom.pdf

Productlinecard:http://www.microchip.com/1010/pline/picmicro/index.htmcontainsadetailedtableidentifyingthecapabilitiesoftheMicrochipproductline.

[1-2] AcompletedatasheetformostPICscomprisestwoelements;(a)adetailedfamilyreferencemanualand(b)theparticulardevicedatasheet.MBasicsupportsonlyPICsfromMicrochipsmidrangefam-ilyandtheassociatedPICmicroMid-RangeMCUFamilyReferenceManualmaybedownloadedathttp://www.microchip.com/download/lit/suppdoc/refernce/midrange/33023a.pdf.Thisisa688-pagedocument,inalmostmindnumbingdetail,butnonethelessisanessentialreferencetoacompleteunderstandingofPICs.ForindividualPICfamilymemberdatasheets,theeasiestsourceistogotohttp://www.microchip.com/1010/pline/picmicro/index.htmandselecteitherthePIC12orPIC16groupandfromthatlinkthenselecttheindividualPICdevice.

Generalnoteonwebaddresses:Manufacturersperiodicallyreorganizetheirwebsites,sotheURLsinthisbookmaychangefromthosegivenasreferences.Thedocuments,however,maybeeasilyfoundthroughthemanufacturershomepagesearchfunction,orthroughageneralsearchenginesuchasGoogle.

10

CHAPTER 2MBasicCompilerandDevelopmentBoards

TheCompilerPackage

ANoteonCompilerVersionsBythetimethisbookispublished,BasicMicrowillhavereleasedanupdatedMBasiccompiler(version5.3.0.0)andrationalizeditscompilerfamily,droppingitsstandardversioncompiler,makingtheformerprofessionalversionitsflagshipPICcompiler.(Ifyouarestillusingversion5.2.,checkwithBasicMicroforupgradeinformation.OwnersofMBasicProfessionalversion5.2qualifyforafreeupgrade,whileMBa-sicStandardownersqualifyforareducedpriceupgradetoMBasic-Professional.)Inaddition,BasicMicrohasamadeavailableafreeversionofitsMBasicProfessionalcompiler,MBasic876ontheCD-ROMas-sociatedwiththisbook.MBasic876isacomplete,100%functionalversionofMBasicProfessional,limitedtoworkingonlywiththe16F876and16F876Adevices.

AllprogramsinthisbookwereoriginallydevelopedandtestedwithMBasicProfessional,version5.2.1.1andhavebeenverifiedwithapre-releaseversionof5.3.0.0.However,bug-fixesandothertweakingtotheofficialreleaseversion5.3.0.0mayoccurthatintroduceminorincompatibilitiesbetweenthecodeinthisbookandBasicMicrosultimatelyreleasedcompiler.TheCD-ROMassociatedwiththisbookprovidesboth5.2.1.1-compliantand5.3.0.0-compilantsourcecode.Chapter29summarizesthedifferencesbetweenver-sion5.3.0.0and5.2.1.1.

Unlessspecificallynoted,thisbookassumesyouareusingMBasicorMBasic876,version5.3.0.0.Theprintedprogramlistingsareforversion5.3.0.0.

MBasicCompiler

Asusedinthisbook,BasicMicrosMBasiccompilercomprisesthreemainelements:

1. MBasicCompilerSoftwareFromversion5.3.0.0onward,BasicMicrooffersoneversionofitsMBa-siccompiler,theProfessionalversion.MBasicrunsunderMicrosoftsWindowsoperatingsysteminanyversionfromWindows95toWindowsXP.ThecomputerrequiresanRS-232portforconnectiontotheISP-PROprogrammerboard.AsecondRS-232port,althoughnotessential,isusefultocaptureanyserialinformationfromtheprogramyouaredeveloping.Ifyourcomputerdoesnothaveasecondserialport,butdoeshaveaUSBport,youmaywishtoaddoneusinganinexpensiveUSB-to-serialconverter.

2. ISP-PROProgrammerMBasic,aftertheassemblystagecompletes,generatesMicrochip-compatiblestandardHEXcodefilethatmustbeloadedintothePIC.BasicMicrooffersaprogrammer,theISP-PRO,wellintegratedwiththeMBasiccompilerthatautomaticallyloadsHEXcodefile.AmajorplusofBasicMicrosISP-PROisreal-timedebuggingthroughitsin-circuitdebuggingorICDcapabil-ity.Althoughitwouldbepossibletosubstituteathird-partyprogrammerfortheISP-PRO,losingbothseamlessintegrationwiththecompilerandICDabilitymorethanoffsetsanycostsavings.TheISP-

MBasicCompilerandDevelopmentBoards

11

PROcommunicateswiththecomputerrunningMBasicviaanRS-232cable,andwiththePICtobeprogrammedthrougha6-wireRJ11telephone-typecableforBasicMicrosdevelopmentandprototypeboards,ora10-pinstandardizedheaderforotherboards.

3. DevelopmentBoardBasicMicrooffersplugboardstyledevelopmentboardsandsolder-inprototypeboardsfor8-and18-pinand28-and40-pinPICs.TheexperimentsinthisbookassumetheuserhasBasicMicrosdevelopmentboards.TheseboardshaveanRJ11connectorfortheISP-PROconnectionandanuncommittedRS-232portthatmaybeusedbythePICforcommunicationstotheoutsideworld.

NoteonSerialPorts:ThesinglelargestsourceoftroublereportedincallstoBasicMicroshelplineconcernsunreliableserialportconnectionswithlaptopcomputers.Thebuilt-inserialportonmanylaptopcomputerscannotreliablyoperateat115.2kb/s,thedefaultspeedatwhichthePC-to-ISP-PROcommunica-tionslinkoperates.Inthosecases,BasicMicrosuggestsusinganinexpensiveadd-onUSB-to-serialadaptertosubstituteforthebuilt-inserialportandrecommendsBafoTechnologiesBF-180USB-to-serialadapter.AslightlymoreexpensivealternativethatIhavehadreliableresultswithisBelkinsF5U109,soldasaUSBPDAAdapter,butwhichis,infact,astraightUSB-to-serialadapter.ManyotherUSB-to-serialadapterslikelywillprovidereliableresults.

Inadditiontothedevelopmentandprototypeboards,theISP-PROiscompatiblewithBasicMicrosUniversalAdapter.TheUniversalAdapter,however,doesnotcontainanoscillatorortheothercircuitryneededtoactuallyrunaPICprogram,andisintendedforprogrammingonly.

BASICandItsEssentials

ThisbookisnotintendedtoteachBASICprogrammingfromthegroundup.TherearemanygoodBA-SICprogrammingforthebeginnerbooksandweassumethereaderhasatleastpassingfamiliaritywithprogramcontrolstatements,mathematicproceduresandvariableassignmentandstructure.ItalsoassumesthereaderhasinstalledtheMBasiccompiler(eitherthefullversionorMBasic876,version5.3.0.0asofthedateofwriting)andhasfamiliarizedhimselfwiththefirst80pagesorsointheMBasicUsersGuide.Incidentally,becauseMBasicis,insomerespects,areturntotheearlydaysofmicrocomputerlanguageimplementation,Ivefound20-yearoldreferencedocumentsforIBMsPersonalComputerBASICbenefi-cialinrefreshingmymemoryonsomeofthefinerpointsofBASICsyntaxorprocedureandofconsiderablymorehelpthanmodernbooksdetailing,forexample,VisualBasic.Avisittoyourlocalusedbookstoremayturnupusefulreferencematerial.Iveprovidedthenamesofafewofmyfavoritelong-out-of-printBASICreferencesinthischaptersreferencesection.

Asaguidetofindingtheappropriateprocedure,Table2-1groupsMBasicscommandsintoalogicalclassification.

Table2-1:TaxonomyofMBasicfunctionsandprocedures.Group Procedure Group Procedure

ProgramFlow Repeat/UntilWhile/WENDDo/WhileFor/NextIf/Then/Else/EndIfGoToGoSub/ReturnBranch

HardwareRelated ADINADIN16CountHPWMSetCaptureGetCaptureSetCompare

Figure2-1:ISP-PROandRJ-11jumpercable.

Chapter2

12


PinRelated ButtonLowPulsInPulsOutRCTimeReverseToggleSetPullupsINxxOutxxDirxx

Miscellaneous DeBugEndLetNapSleepStop

EEPROM DataReadReadDMWriteWriteDM

Variables ClearSwap

I/O I2CinI2CoutOwinOwoutSerDetectSerInSerOutShiftInShiftOutHSerInHSerOut

SoundandSoundRelated DTMFOutDTMFOut2FreqOutPWMSoundSound2

LCD LCDWriteLCDReadLCDInit

DataTable LookDownLookUp

Timing PausePauseUsPauseClk

MemoryRelated PeekPoke

RandomGenerator Random ProgramMemory ReadPMWritePM

OnReset OnPOROnBOROnMOR

ExplicitExternal

DeviceSupport

ServoSPMotorXinXout

Interrupts EnableDisableOnInterruptSetExtIntSetTmr0SetTmr1SetTmr2IsrASMGetTimer1

Assembler ASM{}ISRASM


13


CommandModifiers DecHexBinStrSdecShexSbinIhexIbinISHexISBinREPRealWaitStrWaitSkip

MathOperators

and

Functions

+-*LowMultHighMultFractionalMult///ABSSINCOSDCDSQRBIN2BCDBCD2BINMaxMinDigRev

BitwiseOperators !&|^>>

=

LogicalOperators AndOrXorNotAndNotOrNotXor

FloatingPointConversion ToIntToFloatFloatTable

DevelopmentBoardsBasicMicroofferstwobreadboardstyledevelopmentboards;models0818for8-and18-pinDIPPICs,(Figure2-2),andthe2840for28and40-pinDIPPICs,(Figure2-3).Bothboardshaveasmallsolderlessplug-inareaforadditionalcomponentsandarefullassembledwithsurfacemountcomponents.SocketsareinstalledforthePICs.Anexpandeddevelopmentboard,isunderdevelopmentandmaybeavailablebythetimethisbookispublished.

Figure 2-2: BasicMicros 0818 developmentboard.

Figure 2-3: BasicMicros 2840 developmentboard.

Additionally,BasicMicroofferscorrespondingsemi-permanentprototypeboards,models08/18,Figure2-4and28/40,Figure2-5differingfromthedevelopmentboardsinthatadditionalcomponentsaretobesolderedinratherthanpluggedintoasolderlessbreadboard.Thesearesoldasbareboards,butBasicMicroalsooffersaninexpensivecompletepartskit.Theprototypeboardsusethrough-holecomponents.

Chapter2

14

Allfourboardspermitin-circuitprogrammingthatis,thePICmaybeprogrammedwithoutremovingitfromyourboard,ordisconnectingitspinsfromwhateveryoumayhaveconnectedtothem.Figure2-6,asimplifiedblockdiagramofthe28/40prototypeboard,showshowthisispossible.Threeofthepinsrequiredforprogramming,RB4,RB6andRB7,areswitchedthrougha74HC4053analogmultiplexer/de-multiplexerbetweentheirnormalconnectiontothePICpinheaderandtheRJ11socketthatconnectstotheISP-PROprogrammer.Forourpurpose,the74HC4053canberegardedasanelectronicthree-poledoublethrowswitch,controlledbytheISP-PRO.TheMCLR(masterclear)pinisthefourthcon-nectionrequiredforprogrammingandisdirectlyconnectedtotheRJ11programmingsocket.

The0818and08/18boardsfollowasimilardesign,butwithextraconfigurationjumpersnecessitatedbythemultiplefunc-tionsMicrochipassignedtocertainpinsofPICsproducedin8and18-pinpackages.The0818and08/18datasheetsshouldbeconsultedbeforeprogrammingthesesmallPICs.

AllfourboardsbringthevariousPICpinstologicallylabeledheaders;forexample,A0,A1,soyoudonthavetocontinuallycross-referencephysicalpinnumberswiththeirlogicalassignments.

InworkingwithBasicMicrosdevelopmentboardsandISP-PROprogrammerwatchoutforthefollowing:

Thesearesoldasbareboards,withunprotectedtracesonthebottom.Dontputthemdownonconductivesurfacesortheboardmaybedamagedandwatchforstraywiresorcomponentleadsaswell.(IwatchedmyISP-PROboardbedraggedbyitsserialcableacrossthemetaledgeonthetableandlookedonhelp-lesslyassparksflew.Needlesstosay,theISP-PROdidntworkafterthat.)Ithelpstoaddsmallstick-onrubberfeettothebottomofallboards.

Itispossibletodamagethe74HC4053electronicswitch,asisratedatamaximumswitchedcurrentof25mA.ThemostlikelydamagescenariocomesfromforcingthePICtosinkexcessivecurrent.Additionally,unlikeamechanicalrelay,the74HC4053introducesapproximately80to100ohmsofseriesresistance.

AnotherdifficultybeginnersoftenhaveisconfusingVDDandVSSwhenwiringcircuits.VSSisgroundinBasicMicrosdevelopmentboards.VDDisthesupplyvoltageandis+5voltsinthedevelopmentboards.Thusaschematicreferenceto+5VisthesameasVDDandareferencetogroundcorrespondstoVSS.(Thisterminol-ogycomesfromVDDasthedrainvoltageandVSSasthesourcevoltageforafieldeffecttransistor,thebasicbuildingblockofPICs.)

Figure 2-4: Basic Micros 08/18 prototypeboard.

Figure 2-5: Basic Micros 28/40 prototypeboard.

Figure 2-6: Simplified block diagram of 28/40prototypeboard.


15

ProgrammingStyleEveryprogramprintedinthetextisalsoprovidedasafileintheaccompanyingCD-ROMwithtwoversionssuppliedtheoriginallydevelopedprogramscompatiblewithMBasicversion5.2.1.1.andarevisedver-sioncompatiblewith5.3.0.0.TheremaybedifferencesbetweentheprintedprogramandtheCD-ROMforseveralreasons:

TheCD-ROMisquickertoupdateandmayhavealaterorcorrectedversionofthetextprogram. Pagewidthandoveralllengthrestrictionsmakeitnecessarytolimitthecommentsandblankspaces

usedontheprintedpage.Thedatafileshavenosimilarrestrictionandhencemayhaveadditionalcom-mentsandmaybeformattedforgreaterreadability.(AlthoughnotdocumentedintheUsersGuide,MBasicusestheverticalbar|asacontinuationsymbol,thusallowingonelogicallineofBASICcodetobesplitovertwoormorephysicallines.)

StandardProgramLayout

Asanaidinreadabilityandmaintainability,Iliketofollowastandardlayoutwhenprogramming,asexem-plifiedinthefollowingtemplate:

;ProgramSample.BasFilename;Version1.00;14September2003originalversion;;Constants;-----------------Defineconstantshere

;Variables;-----------------Declarevariableshere

;Initialization;--------------Initializationcodeherethiscodeisexecutedonlyonce

Main;---------MaincodesegmenthereIfsomethingGoSubSub1IfsomethingelseGoSubSub2IfsomethingtotallydifferenthappensGoSubSub3GoToMain;ifappropriatetohaveacontinuousloop

Sub1;----- SubroutinecodehereReturn

Sub2;----- SubroutinecodehereReturn

Sub3;----- Subroutinecodehere IncludesGoSubSubSub1Return

SubSub1;------ SubroutinecodegoeshereReturn

End

Chapter2

16

Thestructureislogical;firstdefineconstantsandvariablesandconductanynecessaryinitialization,thenwritethemainprogramsegment.Iusesubroutinesasnecessary,withthegoalofkeepingthemainsegmentshortandtothepoint.MBasichasnorestrictiononthenumberofsubroutinesthatmaybenestedsoonesubroutinemaycallanother.

Withversion5.3.0.0,MBasicintroduceduser-definedfunctions,albeitwithglobal,notlocal,variables.Thisfeaturewasaddedtoolatetobeusedintheprogrammingexamples,exceptforChapter29.

Constants,VariableandSubroutineNames

Intelligentlyselectingconstant,variableandnamesaidsprogramreadability.MBasicpermitsvariablesandconstantstohavenamesupto1024characterslong,shouldyousowish.(MBasichasseveralhundredreservedwordsandyoushouldntusethesenames.Inmostcasesyouwillreceiveawarningorerrormes-sageifyoutrytoredefineareservedword.)Allnamesarecaseinsensitive,sowecanusecapitalizationtoimprovereadabilitywithoutworryingaboutconsistency.ThenamingconventionsIvedevelopedinclude:

Indexorcountingvariables,forexample,controlvariablesusedinFor/Nextloops,startwithlettersintherangein.(Yes,thisisaholdoverfromtheearlydaysofFORTRANwhenintegervariablenameshadtostartwithoneoftheseletters.)Keepthesenamesshort,particularlyiftheywillbeusedfrequent-ly.Inmanycases,thesinglelettersi,jnareperfectlysuitable.

Namesshouldreflectcontentsoractivities,withoutbeingoverlylong.SupposeweusetheA/Dconvert-ertoreadavoltagefollowedbyasubroutinecalltoaveragethisreadingwiththelast15readingsthatis,amovingaverageof16readingsandthattheindividualreadingisntelsewhereused.Sincethevolt-agevaluebeingreadwillbediscardedaftertheaveragingprocess,wemayuseTempVolt,sotheA/Dreadstatementwouldbe:ADINAN0,CLK,ADSETUP,TempVolt.Iliketonamevariablesthathavelimitedscopewithatwo-partname,startingwithTemp.Tomakethenamemorereadable,useupperandlowercase,thusTempVoltiseasiertoreadthantempvoltorTEMPVOLT.Or,insertanunder-scoreasaseparator;Temp_Volt.(Permissibleseparatorcharactersare_,@,$,%,?and`.)Subroutinesshouldbenamedaccordingtotheactivityperformed,inthisexample,TakeAverageisanappropriatename,orevenTakeAverageVolt.IwouldreservethenameAvgVoltforthevariableholdingtheaverageofthelast16readings,thuskeepingthesuffixnameVoltandchangingtheprefixtodescribethetypeofvoltageparameterinthevariable.Short,conciseandinformativevariablenamescanoftenbeconstructedoftheformadjectivenounwhilesubroutinenamesareoftenoftheformverb-nounwheretheverbdescribestheactionandthenoundescribesthesubjectoftheaction.

Althoughverylongnames,suchasAverageTheLast16VoltageReadingsmayseemdescriptiveatfirst,theyactuallyhinder,ratherthanassistcomprehensioniftheyareusedwithabandon.

Theseareguidelines,nothardandfastrules,andevenmyobservanceisnt100%,butfollowingalogicalcon-sistentnamingapproachwillpaydividendsinthelongrunintermsoffewererrorsandimprovedreadability.

BuildingtheCircuitsandStandardAssumptionsInadditiontotheMBasiccompiler(eitherthefullorMBasic876freeversions),anISP-PROprogrammeranda2840developmentboard,andanyassociatedpartsrequiredforspecificprojects,youshouldhaveaccessto:

Asecondlargerplugboardtoholdoverflowcircuitry. Assortedjumperwires.Youcanpurchaseakitofjumperwires,ormakeyourownfromashortlength

ofscrap25-pairor50-pairtelephonecable. Asecondadjustableregulatedpowersupply,preferablyonethathastwoindependentoutputssothat

positiveandnegativevoltagesmaybeprovided. Adigitalmultimeter. Yourabilitytotroubleshoot,experimentandverifyoperationofcircuitswillbegreatlyenhancedifyou

haveatriggeredoscilloscope.


17

Insteadofbuyingresistorsandcapacitorsoneortwoatatime,considerbuyingassortmentkits.PossiblesuppliersareidentifiedinAppendixA.AlmostallresistorsusedwithaPICwillbe10Korlessinvalueandarewattdissipationrating,soevenalimitedassortmentofvalueswillbequitebeneficial.

Sinceweuseprebuilddevelopmentboards,certainthingsareomittedintheschematicsprovidedinthisbook.

BasicMicrosprototypeanddevelopmentboardsincludebypasscapacitorsontheVDDsupplyheaders.Hence,theywillnotnormallybeillustratedinschematicdiagrams.However,ifpartsofthetestcircuit-ryisbuildonansecondplugboard,orifyouaredesigningaprintedcircuitboardtoholdyourdesign,gooddesignpracticesaysyoushouldliberallybypassVDD.

ThedevelopmentboardsaredesignedforceramicresonatorfrequencydeterminingelementsandareshippedbyBasicMicrowitha10MHzresonator.Thecircuitsandsoftwareinthisbookusea20MHzresonator.Inmanycases,therewillbenodifferenceinperformance,butformaximumcompatibilitywiththeprogramsinthisbook,usea20MHzresonator.Resonatorscostunder$1andareavailablefromsuppliersidentifiedatAppendixA.

ChoiceofPIC

Iveuseda16F877Atodevelopthecircuitinthisbook,butnoneoftheprogramsdependupontheAver-sionsaddedfeatures,soa16F877willworkequallywell.Exceptforthosefewcircuitsthatareinput/outputpinconstrained,youmaysubstitutea16F876or876AinanydesignanduseBasicMicrosfreeMBasic876compilerforalmosteveryprogramwedevelop.

Pins,PortsandInput/OutputSinceeveryusefulprogrammustreadfromorwritetoaPICsinput/outputpins,letssummarizehowMBasichandlespinsandports.ItcanbeconfusingbecausesomepinshavetripleorquadrupleorevenmoredutiesandbecauseMBasicprovidesseveralwaystoaddressanygivenpin.And,thewordpinitselfhasdualusage,asitreferstothephysicalpackaging(an8-pinDIPpackageforexample)andtothosephysicalpinsthatmaybeusedforvariouspurposes.TosimplifyourdiscussionwewilllimitourselvestoPICsthataresupportedbyMBasicandplugintoeitherthe0818or2840developmentboards.

PICscommunicatewithexternalcircuitrythroughintermediaryports.PortsaretreatedinternallybythePICsCPU,andbyMBasic,asbyte(8-bit)variableswitheachbitcorrespondingtoaparticularpin.Forexample,themostsignificantbitinPortBsbytevaluecorrespondstopinRB7,whiletheleastsignificantbitcorrespondstoRB0.(InsomePICs,notallbitsofeachportvariablehavephysicalpinassignments.)

LettersfromAEidentifyports,exceptinDIP8packagedPICswhichhaveonlyoneport,calledGPIO(generalpurposeinput/output).Thus,wehaveGPIO,PortA,PortBPortEaspredeclaredvariablesinMBasic.(Portidentifiersarewrittenwithoutaspace,forexample,PortA,notPortA.)Ofcourse,notallPICsphysicallysupportalloftheseports,andinsomecasesnotalleightbitsofaporthaveassociatedpins.Forexample,thePIC16F876hasPortA(butonlybits05aremappedtopins),PortBandPortC.MBasicsconfigurationfiles,fortunately,ensurethatonlylegitimateportvariablesarepredeclaredfortheparticularPICbeingprogrammed.

Figure2-7illustrates,asanexample,PortBanditspinassign-ments.Eachgeneral-purposeI/Opinisidentifiedwithaconsistentnamingconvention.Forexample,RB0isPortB,bit0.TheRinRBstandsforregister,whichissynonymouswithfileorvariable.MBasicalsopre-definesconstantsassociatedwitheach Figure2-7:PortBtopinassignments.

Chapter2

18

ofthesepins,sowehaveconstantsB0,B1B7availabletous.MBasicgivesusasecondwaytoreferencepinsthroughasequentialnumberingsystem,forexample,A0=0,A1=1upthroughE7=39.Finally,toprovidebackwardscompatibilitywiththeBasicStamp,MBasicincludesthededicatedfunctionsINxx,OUTxxandDIRxxwherexxisthebit,nibble,byteorwordidentifierasreflectedinTable2-2.

Table2-2:PortandbitI/Ovariables,constantsanddedicatedfunctions.Variables Constants DedicatedFunctions

PortataTime

NibbleataTime

BitataTime

INS/OUTS/DIRS

PortVariable

Nibble Port.BitPin

ConstantPin

ValueBit Nibble Byte Word

PortA

PortA.Nib0or

PortA.LowNib

PortA.Bit0 RA0 0 IN0/OUT0/DIR0

INA/OUTA/DIRA

INL/OUTL/DIRL

INS/OUTS/DIRS




PortA.Nib1or

PortA.HighNib


INB/OUTB/DIRB




PortB

PortB.Nib0or

PortB.LowNib

PortB.Bit0 RB0 8 IN8/OUT8/DIR8

INC/OUTC/DIRC

INHOUTH/DIRH

PortB.Bit1 RB1 9 IN9/OUT9/DIR9

PortB.Bit2 RB2 10IN10/OUT10/

DIR10


DIR11

PortB.Nib1or

PortB.HighNib


DIR12

IND/OUTD/DIRD


DIR13


DIR14


DIR15

PortC

PortC.Nib0or

PortC.LowNib

PortC.Bit0 RC0 16

PortC.Bit1 RC1 17

PortC.Bit2 RC2 18

PortC.Bit3 RC3 19

PortC.Nib1or

PortC.HighNib

PortC.Bit4 RC4 20INxx:Readstatus,whetherininputoroutputmode

PortC.Bit5 RC5 21 OUTxx:Writevalue

PortC.Bit6 RC6 22DIRxx:Setdirection1=input,0=output

PortC.Bit7 RC7 23

(continued)


19

Table2-2:PortandbitI/Ovariables,constantsanddedicatedfunctions.Variables Constants DedicatedFunctions

PortataTime

NibbleataTime

BitataTime

INS/OUTS/DIRS

PortVariable

Nibble Port.BitPin

ConstantPin

ValueBit Nibble Byte Word

PortD

PortD.Nib0or

PortD.LowNib

PortD.Bit0 RD0 24xxasappropriateforbit,nibble,byteorword

PortD.Bit1 RD1 25

PortD.Bit2 RD2 26Note:DIRxxcommandisreversedfromBasicStamp

PortD.Bit3 RD3 27

PortD.Nib1or

PortD.HighNib

PortD.Bit4 RD4 28

PortD.Bit5 RD5 29

PortD.Bit6 RD6 30

PortD.Bit7 RD7 31

PortE

PortE.Nib0or

PortE.LowNib

PortE.Bit0 RE0 32

PortE.Bit1 RE1 33

PortE.Bit2 RE2 34

PortE.Bit3 RE3 35

PortE.Nib1or

PortE.HighNib

PortE.Bit4 RE4 36

PortE.Bit5 RE5 37

PortE.Bit6 RE6 38

PortE.Bit7 RE7 39

MBasicpermitsustoreferenceaportorapinasanaddressorasavariable.Asanaddress,theportorpinisanargumenttocertainfunctions.Asavariable,thevalueoftheport(eitherinreadingorwriting)canbeusedlikeanyothervariable.TherearealsothededicatedfunctionsidentifiedinTable2-2thatoperateonspecificportsorpinswithoutanexplicitportorpinreference,suchasIN0.WemustrememberthatMBasicautomaticallyinitializesallI/Opinsasinputsandthatbeforereadingfromorwritingtoaportorapinwemustfollowsomesimplerules:

First,setthedirectionoftheportorpintobeeitheraninputoroutput;

Second,readtheportorpinifaninput,orwritetotheportorpinifanoutput;

or,

Readfromorwritetoaportorpinwithaprocedurethatautomaticallysetsthedirection.

OutputMode

Letsseehowmanydifferentwayswecanassignapintoanoutputandtomakeitsvalue0.WellusepinRB0asourexample.

;DirectPinAddressing;---------------------OutputB0 ;Firstmakeitanoutput.B0isaconstantPortB.Bit0=0 ;PortB.Bit0isavariable

Dir8=0 ;Specialpurposefunction,DIR8isforpinB0Out8=0 ;LikewiseforOut8

Chapter2

20

LowB0 ;Lowfunctionautomaticallymakesitanoutput ;noneedtoseparatelymakeitintoanoutput

Output8 ;B0isanaliasfor8socanuse8directlyPortB.Bit0=0 ;Makethevariableassignment

Low8 ;B0isanaliasfor8socanuse8directly ;LOWswitchestooutputmodeandoutputs0

TRISB.Bit0=0 ;TRISBvariablecontrolsPortBI/Odirection, ;0=output&1=input.PortB.Bit0=0 ;PortB.Bit0isavariable

;Byteatatimeaddressingtodealwithmultiplepins;inoneinstruction;----------------------------------------------------TRISB=%00000000 ;Setsall8pinsto0,i.e.,outputPortB=%00000000 ;Assignall8bits(pins)to0.

DIRH=%00000000 ;Makeall8PinsinPortBoutputOUTH=%00000000 ;Setall8bits(pins)to0

InputMode

TomakeRB0aninputandreaditsvalue,wehavethechoiceofasimilarsetofoptions:;DirectPinAddressing;Assumewehavealreadydeclared:; BitVarVar Bit; ByteVarVar Byte;toholdthevaluebeingread;---------------------InputB0 ;Firstmakeitaninput.B0isaconstantBitVar=PortB.Bit0 ;PortB.Bit0isavariable

Dir8=1 ;Specialpurposefunction,DIR8isforpinB0BitVar=In8 ;LikewiseforIN8

Input8 ;B0isanaliasfor8socanuse8directlyBitVar=PortB.Bit0 ;Makethevariableassignment

TRISB.Bit0=1 ;TRISBvariablecontrolsPortBI/O ;direction,0=output&1=input.BitVar=PortB.Bit0 ;PortB.Bit0isavariable

;Byteatatimeaddressingtodealwithmultiplepins;inoneinstruction;----------------------------------------------------TRISB=%11111111 ;Setsall8pinsto1,i.e.,inputByteVar=PortB ;Readall8bits(pins)intoByteVar.

DIRH=%11111111 ;Makeall8PinsinPortBinputByteVar=INH ;Readall8bits(pins)intoByteVar

PinVariablesvs.Addresses

Onecommonerrorbybeginnersisconfusingpinvariableswithpinaddresses.ThefunctionsOutput,LowandInputrequireapinaddressastheirargument.ThepinaddressmaybeoneofMBasicspre-definedconstants,forexample,B0,oritsequivalentnumericalvalue,8.Thepinaddressmayalsobethevalueofavariable,suchas:

ForI=B0toB7 ;Igoesfrom8(B0)to15(B7) LowI ;MakesB0low,thenB1throughB7sequentiallyNext

IntheLowIstatement,LowoperatesonthevalueofI,whichitinterpretsastheaddressofapin.WhenIis8,forexample,LowoperatesonpinRB0.Thus,theabovecodefragmentisidenticalwith:


21

ForI=8to15 LowINext

Pinvariablesareusedtoreadthevalueofapinorofaportandtowritetoapinorportviaanassignment(the=sign).ThuswehaveByteVar=PortB,orPortB=$FF.WealsomayusePortBlikeanyotherbytevariable,suchasx=2*PortB.

IfwetrytoreadthevalueofpinB0asaninputwiththestatementBitVar=B0,thecompilerwillproducenoerror,butBitVarwillnotholdthedesiredresult.Rather,thisstatementisidenticalwithBitVar=8.Iftestingforapinvalueconditioninaloopstatement,itsimportantthatthevariableconstructbeused.

;TotestPinB0;--------------IfPortB.Bit0=1Then;executecodegoeshereEndIf;Thefollowingcodewillcompilebutwontwork;sinceitsthesameaswritingIf(8=1),whichisalwaysfalseIfB0=1Then;executecodegoeshereEndIf

Finallyitspossibletoreadfromapinorportthatissetforoutputinwholeorinpart,andtowritetoapinorportthatissetforinputinwholeorinpart.Noerrormessagewillbegenerated.Ifyouareexperiencingstrangeorunstableresultsreadingorwritingtopinsorports,checktoensurethecorrectdirectionissetandthatyouarecorrectlyusingpinvariablesandpinconstants.

PICsequippedwithanalog-to-digitalconvertersapplythedesignatorsAN0,AN1topinsthatalsohaveananalogfunction.Thus,a16F876pinnameRA0/AN0indicatesthatthepinhasthreepossibleuses:digitaloutput,digitalinput(RA0)andanalog(AN0)input.TheprocessofassigningapintobeananaloginputisdiscussedindetailinChapter11.

RunTimevs.ProgramTimePinAssignments

Allthepinassignmentswehavediscussedtothispointareruntimealterable,i.e.,theirstatusmaybealteredbytheprogramonthefly.Inonepartofyourprogramapinmaybeaninputandlaterintheprogramthesamepinmaybeanoutput.However,insomePICsmostoftenthoseinthe8and18-pinpackagescer-tainpinconfigurationsmayonlybeestablishedatprogramtime,ataskusuallyaccomplishedviaanoptiondialogboxinMBasicbeforecompilingyourcode.(ThispermitsMicrochiptomaketheirsmallerpackagedevicesmoreflexible,butatthecostofconfusiontobeginningprogrammers.)Then,dependingupontheprogramtimeconfiguration,furtherruntimechangesmaybepossible.ProgramtimepinsetupishighlydevicespecificandreferencetothedatasheetforyourspecificPICwillbebeneficial.

Wellexplorethedifferencebetweenruntimeandprogramtimealterablepinsinthecontextofthe12F629,whichhas3pinsthatmustbeconfiguredatprogramtime:

12F629ExampleofPinsConfiguredatProgramTime

PinName ProgramTimeConfiguration RunTimeConfiguration

GP3/MCLR/VppGP3(general-purposeI/O)

GP3:InputGP3:Output

MCLR/Vpp(masterclear/Vprogram) None

GP4/T1G/OSC2/CLKOUT

GP4(general-purposeI/O)GP4:InputGP4:Output

T1G(timer1gate)

OSC2(secondresonatorconnection) None

CLKOUT(clockout) None

Chapter2

22

Figure 2-8: Program time pin optionsfor12F629.

12F629ExampleofPinsConfiguredatProgramTime

PinName ProgramTimeConfiguration RunTimeConfiguration

GP5/T1CKI/OSC1/CLKIN

GP5(general-purposeI/O)GP5:InputGP5:Output

T1CKI(Timer1clockin)

CLKIN(externalclockinput) None

OSC1(firstresonatorconnection) None

IftheGP3/MCLR/Vpppinisdefinedatprogramtimetobeagener-al-purposeI/Opin,itmaybeusedforinputoroutputexactlyaswehaveearlierdiscussed,andchangedfrominputtooutputunderpro-gramcontrol.However,ifatprogramtimeitisdefinedasMCLR,itisunavailableforanyotherpurpose.ThisselectionisaccomplishedwiththeMCLRcheckboxfoundinMBasicsConfigurationdialogbox,asshowninFigure2-8.

Thetwooscillatorpinsalsomustbedefinedatprogramtime,butarelinked.Ifyouplantouseanexternalresonatororcrystal,theOSC1andOSC2pinconfigurationmustbeactive.Ifyouplantouseanexternalclocksource,thentheCLKINoptionmustbeactive.IfyouwishtousetheinternalRCoscillator,thentheCLKOUTpinmayeitherbeGP5orOSCOUT.IfanexternalRCoscillatorisused,theRCnetworkmustconnecttotheOSC1pin.Table2-3showshowtheseoptionsinteractandhowtheyareselectedintheMBasicconfigurationboxofFigure2-8.(TheMBasicconfigurationoptionscorrespondtothefirstcolumninTable2-3.)

Table2-3:ConfigurationDialogfor12F629OscillatorConfiguration.Configuration

DialogBox

Oscillator

Configuration GP4/T1G/OSC2/CLKOUTFunction GP5/T1CKI/OSC1/CLKINFunction

LowPower LP OSC2crystalconnection OSC1crystalconnection

External XT OSC2crystalconnection OSC1crystalconnection

HighSpeed HS OSC2crystalconnection OSC2crystalconnection

ExternalClk EC GP4(general-purposeI/O) CLKIN(externalclockinput)

IntRConGP4 INTOSC GP4(general-purposeI/O) GP5(general-purposeI/O)

IntRConClkOut INTOSC CLKOUT(clockwaveformoutput) GP5(general-purposeI/O)

ExtRConGP4 RC GP4(general-purposeI/O) CLKIN-RCcircuitonpin

ExtRConClkOut RC CLKOUT(clockwaveformoutput) CLKIN-RCcircuitonpin

Furthercomplicatinganalreadycomplexmatter,anexternalclocksourcemaybeusedintheLP,XTandHSmodesbyfeedingitintoOSC1,inwhichcase,OSC2isunused.TheLP,XTandHSmodessetinternalparametersintheoscillatorsectionofthe12F629andestablishthemaximumresonatororcrystalfrequencyandassociatedcapacitorvalues.Section9ofMicrochipsPIC12F629/675DataSheetshouldbeconsultedforspecifics.

LVPProgrammingPinSelection

Onecompiletimefeaturesharedby16F876/877chips(includingtheAversions),alongwithmanyotherflashprogrammemoryPICs,isthelowvoltageprogramming(LVP)option.Historically,flashmemoryhasrequiredapplicationofaprogrammingvoltagetwoorthreetimesthatofthenormaloperatingvoltage,


23

typically12VforaPICoperatingwithVDDof5V,knownashighvoltageprogramming(HVP).NewerPICs,suchasthe16F876/877/876A/877AmaybeoptionallyprogrammedinLVPmode,usingonly+5V.WhetheraPICthatsupportsLVPactuallyhasLVPenabledisdeterminedbyaconfigurationbit,thevalueofwhichiskeyedtotheLVPcheckboxinMBasicsconfigurationsetupdialogboxseeninFigure2-8.IfthechipdoesnotsupportLVP,asistrueinFigure2-8,theLVPcheckboxisgrayedout.

ToensuremaximumflexibilitywhenprogrammingbotholderandnewermodelPICs,BasicMicrosISP-PROandits0818and2840DevelopmentBoardsusehighvoltageprogrammingandfortheprogramsinthisbookyoushouldnotselectLVPmodeinMBasicsprogrammingoptions.MicrochipenablesLVPaspartof

themanufacturingprocess,sowhenprogramminganewPICforthefirsttimeyouwillfinditnecessaryto

cleartheLVPselectionboxinMBasicsconfigurationmenu,ifthatmodelPIChasLVPfunctionality.

BasicMicrosISP-PROdoesnotsupportLVPandprogramsonlyusingHVPmode.But,sinceaPICwithLVPenabledisstillprogrammableviaHVP,youcan,nonetheless,selectLVPandprogram16F876/877/876A/877AchipswithMBasicandtheISP-PRO.However,ifyoudoso,pinRB3becomestheLVPcontrolpinandisnolongeravailableasageneral-purposeI/Opin.(ThespecificpinusedforLVPcontrolvaries;forexample,a16F628usesRB4.)NoteveryLVP-capablemodelPICbehavessonicelyandyoumayfindsomemodeldevicesrefusetoprogramifyouinadvertentlyleavetheLVPoptionselected.IveevenseendifferentsamplesofthesamemodelPICbehavedifferentlywiththeLVPoptionselected.Inthiscase,clearingtheLVPcheckbox,followedbyseveralcyclesofMBasicserasefunctionusuallyrestoresprogrammability.

WeakPull-Up

Onelastremarkandwemayleavethisoverlylongdiscussionofpins.ManyPICshavebuilt-inweakpull-upresistorsforPortB,usablewhensettobeaninput.Welldealwithfloatinginputgatesandtheneedforpull-upresistorsinChapter4,butMBasicsprocedureforcontrollingPortBsinternalpullupsisSetPullUpswheremodeisoneoftwopre-definedconstants,Pu_OfforPu_Onforde-activatingoractivating,respectively,internalpull-upresistors.Pull-upresistorsforalleightpinsofPortBareactivatedordeactivatedbythiscommand,notindividualpins.ForPortBpinsthataresettobeoutputs,SetPullUpshasnoeffect.

Pseudo-CodeandPlanningtheProgramIndescribinganalgorithmorevenacompleteprogram,wewilloftenuseamixtureofEnglishandMBasicstatementscalledpseudo-code.Pseudo-codeisausefultoolwhendevelopinganideabeforewritingalineoftruecodeorwhenexplaininghowaparticularprocedureorfunctionorevenanentireprogramworks.TodistinguishitfromMBasicorassembler,pseudo-codewillappearinbold,italicCouriertypeface.

Letsillustratethebenefitofpseudo-codewithasimpleexample.SupposewewishtoilluminateanLEDfor1secondwheneverabuttonispushed.WellassumethatthebuttonisconnectedtotheRB0pinonaPIC,thatpressingthebuttontakesRB0lowandthattheLEDisilluminatedbytakingpinRB1high.Afteranybuttonpush,theprogramrepeatsandwaitsforthenextpush.(Wellignorebuttondebounce,multiplebuttonpressesandafewotherreal-worldconcerns.)Apseudo-codeversionofourprogramis:

InitializationRoutineInitializebuttonpintobeaninputInitializeLEDpintobeanoutputSetLEDpintonotilluminateLED

MainProgramLoopStart Readbuttonpinanddeterminestate Ifbuttonnotpresseddonothing Ifbuttonpinispressed,setLEDpintoilluminate Ifbuttonhasbeenpressedwait1second TurnLEDOffafter1secondGobacktoMainProgramLoopandtestfornextpress

Chapter2

24

Thispseudo-codeexampleoffersaeasytounderstandstatementoftheprogramstructureandoncewearesatisfiedthatitslogicmatchesourdesiredoperation,wecaneasilytransformitintoanMBasicprogram,witheachlineofpseudo-codeexpandingintooneortwolinesofrealcode:

;Initialization;--------------InputB0 ;InitializebuttonpintobeaninputOutputB1 ;InitializeLEDpintobeanoutputLowB1 ;SetLEDpintonotilluminateLED

Main;----- IfPortB.Bit0=0Then;Readpinanddeterminestate HighB1 ;Ifpressed,LEDilluminated Pause1000 ;Ifbuttonpressedwait1second LowB1 ;TurnLEDOffafter1second EndIf ;Ifbuttonnotpresseddonothing ;GobacktoMainProgramLoopandGoToMain ;testfornextpress

End

Forallbutthesimplestprograms,Istartwithahighlevelpseudo-codedefinitionofoverallprogramflowperhapsaidedbyasimpleflowchartbutatahighlevelofabstraction.Thefirstpseudo-codedraftconcentratesonthehighlevelprogramflowandlogic,withsubroutines,initialization,input/outputconcernsbeingalineortwoofpseudo-code.Itshowsthedesiredinputandoutputdata,evenifitissomethingassimpleasreaduserskeypadpress.ImayevenwriteanddebugMBasiccodeimplementingthehighleveldesign,substitutingdummysub-routinesforthedetailedones,andhard-codinguserinputs.

Oncethehigh-levelprogramflowisfunctioning,Iwritepseudo-codeforeachmainsubroutine,followedbyanMBasicrealization.Eachsubroutineiswrittenanddebuggedbeforestartingonthenext,totheextentpermittedbytheprogramlogic.Whereonesubroutinedependsonthenext,followatopdownapproach.

Ifyouhavetoboildownwritinggoodcodeintoonerule,itwouldbe:

Thinkfirst,codelater.

Ifwearepermittedafewmorerules,theywouldbe:

Definetheproblem,includingthegoesintosandcomesoutofs,thatis,theinformationtogointotheprogram,suchasswitchreadings,sensorreadingsandtheconditionsthatcausethosereadingstobegener-ated,andthedesiredoutput,suchaslogiclevelpinchanges,analogoutputsthroughadigital-to-analogconverter,andtheactionstheseoutputscause,suchasturningonamotororactivatingasolenoid.

Documenttheproblemandthesolutionandkeepthedocumentationuptodateasyoudevelopanswers,evenifyouareprogrammingforpersonalsatisfaction,oreducationandnotwiththethoughofdevelop-ingacommercialproduct.

Thinkfirst,codelaterthesinglemostimportantthingforaprogrammertodoistoresistthesirencallofwritingcodeandinsteadstudy,understandandplanwhattodo.Codingisoftenthesimplesttaskandcanbealmostmechanical,iftheproblemisfirstproperlyunderstoodanddefined.

Programmodularly,proceedingfromthetopdown,anessentialphilosophyifyouaretoefficientlyproducereadable,stablecode.Itspossibletoprogramfromthebottomup,startingwithdetailsandworkingtowardsageneralstructurethatfitstogetherthedetails,butitsnevertherightwaytopro-ceed.Andifyoudomanagetomakeitwork,achangeindetailscanupsetthegeneralstructureyouvecobbledtogether.Top-downprogrammingismuchmoretoleranttotheinevitablechangesthatoccurasaprojectprogresses.And,writecodeinmodularsubroutines,notasonelargeomnibusprogram.Codedevelopment,maintainabilityanddebuggingareallimmenselyaidedbycodinginsubroutines.Asseen

MBasicCompilerandD