Programming the PIC microcontroller in c.pdf

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Programming฀the฀

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AMSTERDAM • BOSTON • HEIDELBERG • LONDON NEW YORK • OXFORD • PARIS • SAN DIEGO SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO

Newnes is an imprint of Elsevier

Programming฀the฀

PIC฀Microcontroller฀with฀MBasic฀

by฀Jack฀R.฀Smith

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Linacre฀House,฀Jordan฀Hill,฀Oxford฀OX2฀8DP,฀UK Copyright฀©฀2005,฀Elsevier฀Inc.฀All฀rights฀reserved. No฀part฀of฀this฀publication฀may฀be฀reproduced,฀stored฀in฀a฀retrieval฀system,฀or฀฀ transmitted฀in฀any฀form฀or฀by฀any฀means,฀electronic,฀mechanical,฀photocopying,฀฀ recording,฀or฀otherwise,฀without฀the฀prior฀written฀permission฀of฀the฀publisher.฀ Permissions฀may฀be฀sought฀directly฀from฀Elsevier’s฀Science฀&฀Technology฀Rights฀฀ Department฀in฀Oxford,฀UK:฀phone:฀(+44)฀1865฀843830,฀fax:฀(+44)฀1865฀853333,฀฀ e-mail:฀[email protected].฀You฀may฀also฀complete฀your฀request฀online฀฀ via฀the฀Elsevier฀homepage฀(http://www.elsevier.com),฀by฀selecting฀“Customer฀฀ Support”฀and฀then฀“Obtaining฀Permissions.” Recognizing฀the฀importance฀of฀preserving฀what฀has฀been฀written,฀฀ Elsevier฀prints฀its฀books฀on฀acid-free฀paper฀whenever฀possible. Library฀of฀Congress฀Cataloging-in-Publication฀Data ฀ (Application฀submitted.) British฀Library฀Cataloguing-in-Publication฀Data A฀catalogue฀record฀for฀this฀book฀is฀available฀from฀the฀British฀Library. ISBN:฀0-7506-7946-8 For฀information฀on฀all฀Newnes฀publications฀ visit฀our฀website฀at฀www.books.elsevier.com 05฀฀06฀฀07฀฀08฀฀09฀฀10฀฀฀฀10฀฀9฀฀8฀฀7฀฀6฀฀5฀฀4฀฀3฀฀2฀฀1 Printed฀in฀the฀United฀States฀of฀America

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Preface฀... x฀ Acknowledgments฀... xii฀ What’s฀on฀the฀CD-ROM?฀... xiii CHAPTER฀1:฀What฀is฀a฀PIC®_{?฀฀... 1} PICs฀“101”฀... 1 How฀Do฀I฀Tell฀Them฀Apart?฀... 2 Which฀One฀Should฀I฀Use?฀... 4 How฀Do฀I฀Pick฀One?฀... 7 So,฀Which฀One฀Do฀I฀Really฀Want฀to฀Use?฀... 8 Basic฀Micro’s฀MBasic876฀Compiler฀... 8 References฀... 9 CHAPTER฀2:฀MBasic฀Compiler฀and฀Development฀Boards฀... 10 The฀Compiler฀Package฀... 10 BASIC฀and฀Its฀Essentials฀... 11 Development฀Boards฀... 13 Programming฀Style฀... 15 Building฀the฀Circuits฀and฀Standard฀Assumptions฀฀... 16 Pins,฀Ports฀and฀Input/Output฀... 17 Pseudo-Code฀and฀Planning฀the฀Program฀... 23 Inside฀the฀Compiler฀... 25 References฀... 27 CHAPTER฀3:฀The฀Basics฀–฀Output฀... 28 Pin฀Architectures฀... 28 LED฀Indicators฀... 31 Switching฀Inductive฀Loads฀... 34 Low฀Side฀Switching฀... 36 Isolated฀Switching฀... 45 Special฀Purpose฀Switching฀... 50 Fast฀Switching—Sound฀from฀a฀PIC฀... 50 References฀... 51 CHAPTER฀4:฀The฀Basics฀–฀Digital฀Input฀... 53 Introduction฀... 53 Switch฀Bounce฀and฀Sealing฀Current฀... 58 Isolated฀Switching฀... 62

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Reading฀a฀Keypad฀... 63 References฀... 66 CHAPTER฀5:฀LCD฀Modules฀... 67 Selecting฀a฀Display฀... 67 VFD฀Displays฀... 69 Connection฀to฀PIC฀... 69 Hello฀World฀... 72 LCD฀Module฀Memory,฀Shifts฀and฀Lines฀... 74 Font฀Selection฀... 79 Custom฀Characters฀... 80 References฀... 85 CHAPTER฀6:฀Reading฀Complex฀Input฀Switches฀... 86 Pin฀Saving฀Techniques฀... 86 Rotary฀Encoders฀... 91 Reading฀a฀Relative฀Encoder฀... 95 Dual฀Encoders฀and฀LCD฀... 100 References฀... 106 CHAPTER฀7:฀Seven-Segment฀LED฀Displays฀... 107 LED฀Display฀Selection฀... 107 Circuit฀Design฀... 108 References฀... 119 CHAPTER฀8:฀Introductory฀Stepper฀Motors฀... 120 Stepper฀Motor฀Basics฀... 120 Programs฀... 133 References฀... 150 CHAPTER฀9:฀RS-232฀Serial฀Interface฀... 151 How฀to฀Connect฀to฀Your฀PC฀... 151 Voltage฀Levels฀in฀RS-232฀and฀Level฀Conversion฀... 152 Standard฀Pin฀Connections฀... 154 Asynchronous฀Transmission,฀Start฀Bits,฀Stop฀Bits฀and฀Bit฀Order฀... 154 MBasic’s฀Procedures฀for฀Serial฀Communications฀... 156 Programs฀... 159 References฀... 186 CHAPTER฀10:฀Interrupts฀and฀Timers฀in฀MBasic฀... 187 Interrupts฀and฀Timers—Overview฀... 187 Interrupts฀... 188 Timers฀... 194 Capture฀and฀Compare฀... 203 References฀... 210 CHAPTER฀11:฀Analog-to-Digital฀Conversion฀... 211 Introduction฀to฀Analog-to-Digital฀Conversion฀... 211 Resolution฀and฀Accuracy฀... 212 Self-Contained฀DVM฀... 218 References฀... 230

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CHAPTER฀12:฀Digital฀Temperature฀Sensors฀and฀Real-Time฀Clocks฀... 231 DS18B20฀Temperature฀Sensor฀... 231 DS1302฀Real-Time฀Clock฀... 243 Combination฀Date,฀Time฀and฀Temperature฀... 252 References฀... 259 CHAPTER฀13:฀Assembler฀101฀... 260 The฀Basics฀... 260 OpCodes฀... 267 References฀... 280 CHAPTER฀14:฀In-Line฀Assembler฀... 281 Adding฀Assembler฀to฀MBasic฀Programs฀... 281 Bolt-In฀Assembler฀Functions฀... 295 References฀... 316 CHAPTER฀15:฀Interrupt฀Handlers฀and฀Timers฀in฀Assembler฀... 317 ISRASM฀–฀MBasic’s฀Gateway฀to฀Assembler฀Interrupt฀Service฀Routines฀... 317 Program฀Examples฀... 323 References฀... 334 CHAPTER฀16:฀Digital-to-Analog฀Conversion฀... 335 Introduction฀to฀Digital-to-Analog฀Conversion฀... 335 Resolution฀–฀Accuracy฀and฀Signal-to-Noise฀Ratio฀... 336 Henry฀Nyquist฀and฀his฀Sampling฀Theorem฀... 337 DAC฀Circuit฀Design฀... 339 Alternative฀Analog฀Output฀Solutions฀... 352 References฀... 358 CHAPTER฀17:฀DTMF฀Tone฀Decoding฀and฀Telephone฀Interface฀... 360 What฀is฀Touch-Tone฀Signaling?฀... 360 Generating฀Touch-Tone฀Signals฀... 361 Decoding฀a฀Touch-Tone฀Signal฀... 361 References฀... 388 CHAPTER฀18:฀External฀Memory฀... 389 I2_{C-Bus฀Devices฀... 389} Practical฀Use฀of฀External฀EEPROM฀... 403 Parallel฀Access฀Memory฀... 408 References฀... 416 CHAPTER฀19:฀Advanced฀Stepper฀Motors฀... 418 Microstepping฀... 418 Programs฀... 420 References฀... 452 CHAPTER฀20:฀X-10฀Home฀Automation฀... 453 How฀X-10฀Works฀... 453 Programs฀... 459 References฀... 486

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CHAPTER฀21:฀Digital฀Potentiometers฀and฀Controllable฀Filter฀... 487 Getting฀Started฀with฀an฀MCP41010฀... 489 RS-232฀Control฀of฀an฀MCP41010฀... 493 Daisy฀Chaining฀Multiple฀MCP42010฀Devices฀... 498 RS-232฀Command฀of฀Multiple฀Daisy฀Chained฀MCP42010฀Devices฀... 501 Logarithmic฀Response฀for฀Audio฀Volume฀Control฀... 506 Electronically฀Tunable฀Low-Pass฀Filter฀Using฀MCP42010฀... 511 References฀... 515 CHAPTER฀22:฀Infrared฀Remote฀Controls฀... 517 Common฀Encoding฀Standards฀... 518 IR฀Receiver฀... 520 Characterizing฀Wide/Narrow฀Pulse฀Intervals฀... 522 Decoding฀a฀REC-80฀Controller฀... 532 References฀... 541 CHAPTER฀23:฀AC฀Power฀Control฀... 542 Introduction฀to฀Triacs฀... 543 Snubberless฀versus฀Standard;฀dV/dt฀and฀dI/dt฀Issues฀... 545 Triggering฀a฀Triac฀฀... 548 Phase฀and฀Cycle฀Control฀... 549 Power฀Control฀Board฀... 551 Programs฀... 555 References฀... 565 CHAPTER฀24:฀DC฀Motor฀Control฀... 567 Introduction฀to฀Control฀Theory฀... 567 Measure฀Motor฀Speed฀(Tachometer฀Output฀Pulse฀Width)฀... 568 Error฀=฀Target฀Width฀–฀Measured฀Width฀฀... 572 The฀Control฀Algorithm฀... 572 Motor฀Control฀Programs฀... 573 References฀... 594 CHAPTER฀25:฀Bar฀Code฀Reader฀... 595 Bar฀Codes฀“101”฀... 595 Bar฀Code฀Wand฀... 599 Programs฀... 602 References฀... 631 CHAPTER฀26:฀Sending฀Morse฀Code฀... 633 Morse฀Code฀101฀... 633 Programs฀... 635 References฀... 660 CHAPTER฀27:฀Morse฀Code฀Reader฀... 661 Sending฀and฀Receiving฀Morse฀... 661 Tone฀Detector฀Circuit฀... 663 Programs฀... 668 References฀... 689

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CHAPTER฀28:฀Weather฀Station฀and฀Data฀Logger฀... 691 Sensor฀Selection฀... 691 Connecting฀the฀Sensors฀and฀Memory฀... 698 Initial฀Tests฀... 700 References฀... 728 CHAPTER฀29:฀Migrating฀from฀v5.2.1.x฀to฀5.3.0.0฀and฀the฀Undocumented฀MBasic฀... 729 Migrating฀from฀v5.2.1.x฀to฀5.3.0.0฀... 729 Undocumented฀MBasic฀... 733 APPENDIX฀A:฀Parts฀List฀and฀Suppliers฀... 745 Suppliers฀... 745 Generic฀Components฀Required฀... 746 Speciﬁc฀Components฀... 748 APPENDIX฀B:฀Function฀Index฀... 755 About฀the฀Author฀... 760฀ Index฀... 761

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My฀introduction฀to฀computers฀was฀in฀the฀days฀of฀IBM’s฀Model฀29฀card฀punch.฀You฀first฀carefully฀printed฀ your฀FORTRAN฀code฀on฀a฀coding฀sheet,฀then฀punched฀a฀card฀deck฀and฀finally฀walked฀your฀cards฀over฀to฀ the฀campus฀computer฀center.฀There,฀one฀of฀the฀high฀acolytes฀of฀the฀IBM฀360—in฀reality฀a฀grad฀student—ac-cepted฀the฀deck฀with฀a฀faint฀look฀of฀disdain.฀You฀might฀even฀catch฀a฀glimpse฀of฀the฀computer฀itself฀through฀ the฀glass฀wall฀of฀the฀computer฀center.฀The฀following฀day,฀if฀you฀were฀fortunate,฀your฀card฀deck฀was฀ready฀for฀ pick-up,฀wrapped฀in฀the฀green฀bar฀paper฀output฀your฀job฀elicited.฀If฀you฀were฀really฀lucky,฀the฀output฀made฀ sense฀and฀you฀could฀go฀on฀to฀your฀next฀task.฀If฀you฀were฀less฀fortunate,฀the฀printout฀identified฀your฀errors.฀ And,฀if฀you฀were฀really฀having฀a฀bad฀day,฀your฀card฀deck฀was฀hidden฀inside฀an฀inch-thick฀core฀dump฀print-out,฀dense฀with฀hexadecimal฀register฀and฀memory฀values.฀฀ Today,฀we฀have฀as฀much฀computing฀power฀on฀our฀desktops฀as฀was฀behind฀the฀glass฀wall฀when฀I฀was฀punch-ing฀card฀decks.฀Computers฀are฀now฀embedded฀in฀almost฀every฀imaginable฀electronic฀device.฀One฀of฀the฀ pioneers฀in฀embedded฀computers฀was฀General฀Instruments,฀which฀in฀1976฀released฀the฀1650฀“programmable฀ intelligent฀computer,”฀the฀grandfather฀of฀today’s฀PICs.฀(There฀is฀a฀raging฀debate฀among฀the฀cognoscenti฀over฀ the฀“true”฀name฀behind฀the฀PIC฀acronym,฀with฀“peripheral฀interface฀controller”฀often฀being฀cited.฀GI’s฀1977฀ data฀sheet฀for฀the฀PIC1650,฀though,฀confirms฀the฀term฀“programmable฀intelligent฀computer.”฀Microchip฀ Technology฀Incorporated,฀who฀acquired฀GI’s฀PIC฀business฀in฀the฀mid฀1980s,฀wisely฀stays฀out฀of฀the฀debate฀ and฀just฀calls฀its฀products฀“PICmicro®฀microcontrollers.”)฀ This฀book฀focuses฀on฀programming฀Microchip’s฀mid-range฀PIC฀line฀with฀MBasic,฀a฀powerful,฀but฀easy฀to฀ learn฀programming฀language,฀developed฀by฀Basic฀Micro฀of฀Murrieta,฀California.฀Since฀a฀PIC฀by฀itself฀is฀not฀ all฀that฀useful,฀I฀will฀illustrate฀MBasic’s฀abilities฀through฀a฀series฀of฀construction฀projects,฀some฀simple฀and฀ some฀more฀advanced.฀I฀will฀also฀dip฀into฀assembler฀language,฀as฀there฀are฀some฀applications฀that฀require฀us฀ to฀become฀more฀intimate฀with฀the฀PIC’s฀internals฀than฀possible฀in฀MBasic. The฀projects฀assume฀the฀user฀has฀MBasic฀Professional฀version฀5.3.0.0฀compiler,฀the฀associated฀ISP-PRO฀ programmer฀and฀a฀2840฀development฀board,฀all฀available฀from฀Basic฀Micro.฀Almost฀all฀examples฀use฀a฀ 16F877A฀PIC฀and฀a฀20฀MHz฀resonator.฀However,฀both฀the฀code฀and฀supporting฀circuitry฀are฀easily฀portable฀ to฀many฀other฀PICs฀supported฀by฀MBasic.฀More฀importantly,฀almost฀every฀project฀in฀this฀book฀can฀be฀built฀ with฀the฀free฀MBasic876฀compiler฀included฀in฀the฀accompanying฀CD-ROM.฀In฀a฀few฀cases,฀the฀16F876฀ doesn’t฀have฀enough฀I/O฀pins฀to฀support฀the฀project.฀ Reading฀Basic฀Micro’s฀message฀board,฀and฀questions฀from฀beginners฀posted฀to฀the฀PIC฀microcontroller฀ discussion฀list,฀reveals฀a฀need฀for฀information฀showing฀how฀the฀smorgasbord฀of฀functions,฀procedures฀and฀ code฀snippets฀found฀in฀the฀MBasic฀User’s฀Guide฀might฀be฀put฀together฀to฀actually฀do฀something฀useful.฀And,฀ since฀doing฀“something฀useful”฀with฀a฀PIC฀inevitably฀requires฀some฀associated฀circuitry,฀electronics฀ques-tions฀are฀sprinkled฀liberally฀throughout฀these฀fora฀as฀well.฀

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I’ve฀tried฀to฀address฀both฀the฀software฀and฀hardware฀aspects฀of฀working฀with฀PICs,฀with฀my฀imagined฀reader฀ having฀an฀interest฀in฀both฀programming฀and฀electronics,฀but฀without฀specialized฀training.฀Although฀I’ve฀tried฀ to฀err฀on฀the฀side฀of฀inclusion฀over฀brevity,฀this฀book฀can’t฀replace฀a฀basic฀understanding฀of฀electronics,฀nor฀ an฀elementary฀grasp฀of฀how฀one฀goes฀about฀writing฀BASIC฀programs.฀I฀trust฀that฀readers฀experienced฀in฀ electronics฀will฀forgive฀the฀simplifications฀necessitated฀in฀this฀endeavor,฀and฀that฀experienced฀programmers฀ understand฀that฀they฀will฀not฀necessarily฀find฀elegant฀algorithms฀or฀code฀in฀every฀case.฀But,฀this฀work฀is฀not฀ intended฀to฀replicate฀Knuth’s฀The฀Art฀of฀Computer฀Programming,฀nor฀Horowitz฀and฀Hill’s฀The฀Art฀of฀Elec-tronics.฀And,฀I฀couldn’t฀duplicate฀either฀if฀I฀tried฀my฀best฀for฀the฀next฀decade.฀ Finally,฀I’ve฀never฀found฀the฀impersonal฀passive฀technical฀writing฀style฀conducive฀to฀learning฀a฀new฀subject.฀ After฀all,฀“the฀code฀was฀transferred฀to฀the฀PIC”฀isn’t฀what฀actually฀happened฀was฀it?฀Someone—probably฀ you,฀but฀certainly฀not฀some฀disembodied฀entity—programmed฀the฀PIC฀using฀the฀MBasic฀software.฀Why฀not฀ say฀so?฀Likewise,฀although฀we฀know฀that฀a฀PIC’s฀output฀pin฀doesn’t฀“see”฀a฀load฀resistance฀through฀physical฀ eyes,฀these฀anthropomorphic฀analogies฀are฀easier฀to฀understand฀than฀reading฀“the฀equivalent฀resistance฀that฀ would฀be฀measured฀by฀an฀appropriate฀impedance฀measuring฀instrument฀connected฀in฀place฀of฀the฀pin฀and฀ applying฀a฀+5฀volt฀dc฀stimulus฀signal฀to฀the฀load฀resistance.”฀Hence,฀I฀make฀no฀apologies฀for฀the฀chatty฀style. This฀book฀is฀not฀an฀“official”฀publication฀of฀Basic฀Micro,฀and฀its฀contents฀reflect฀my฀views,฀not฀those฀of฀ Basic฀Micro,฀or฀its฀employees฀or฀owners.฀ In฀a฀book฀of฀this฀length฀and฀detail,฀there฀will฀inevitably฀be฀errors฀and฀omissions,฀despite฀the฀best฀efforts฀of฀ the฀author฀and฀editors.฀Some฀are฀the฀unavoidable฀byproduct฀of฀simplifying฀complex฀subjects฀for฀an฀intro-ductory฀level฀presentation฀and฀others฀are฀just฀plain฀dumb฀mistakes.฀Regardless฀of฀the฀category,฀I฀accept฀full฀ responsibility.฀I฀may฀be฀contacted฀by฀e-mail฀at฀[email protected]฀to฀report฀errors฀or฀omissions. ฀ Jack฀Smith฀ ฀ June฀2005,฀Clifton,฀VA฀

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Acknowledgments฀are฀due฀to฀my฀wife฀Janet,฀who฀has฀tolerated฀with฀good฀grace฀the฀innumerable฀hours฀I’ve฀ spent฀in฀the฀basement฀workshop฀or฀in฀front฀of฀the฀computer฀screen.฀I฀also฀wish฀to฀thank฀the฀people฀at฀Basic฀ Micro,฀including฀Nathan฀Scherdin,฀and฀Dale฀Kubin,฀for฀their฀assistance฀in฀writing฀this฀book.฀I฀also฀wish฀to฀ thank฀Larry฀and฀Janet฀Phipps฀for฀the฀hospitality฀shown฀to฀me.฀

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The฀content฀of฀the฀CD-ROM฀was฀developed฀with฀Windows®฀XP,฀and฀has฀been฀veriﬁed฀as฀readable฀with฀ Windows®฀2000.฀It฀has฀not฀been฀tested฀with฀other฀operating฀systems. Its฀contents฀are฀organized฀in฀a฀series฀of฀directories: MBasic876 Basic฀Micro฀Inc.฀has฀provided฀a฀free฀MBasic฀compiler,฀MBasic876,฀with฀all฀features฀of฀MBasic฀Profession-al,฀but฀restricted฀to฀program฀only฀16F876฀and฀16F876A฀devices.฀An฀installation฀program,฀MBasic876_Setup,฀ to฀add฀MBasic876฀to฀your฀computer฀is฀contained฀in฀this฀directory.฀Launching฀MBasic876_Setup฀will฀start฀ the฀installation฀process. The฀directory฀MBasic\Documents฀contains฀the฀MBasic฀User’s฀Guide฀and฀data฀sheets฀on฀Basic฀Micro’s฀฀ programming฀board฀and฀development฀and฀prototype฀boards. Basic฀Micro’s฀website,฀http://www.basicmicro.com/,฀has฀an฀active฀MBasic฀user’s฀forum฀that฀I฀highly฀฀ recommend.฀ Linear฀Technology฀Circuit฀Simulation฀Software Linear฀Technology฀Corporation฀has฀provided฀two฀programs฀for฀circuit฀simulation.฀Both฀programs฀were฀used฀ in฀developing฀and฀illustrating฀the฀circuits฀in฀this฀book.฀ The฀directory฀Linear฀Technology฀Circuit฀Simulation฀Software\FilterCAD฀contains฀the฀installation฀program,฀ FilterCADv300.exe,฀which฀installs฀FilterCAD฀version฀3.00฀on฀your฀computer.฀FilterCAD฀is฀a฀powerful฀tool฀ for฀designing฀and฀simulation฀active฀ﬁlters. The฀directory฀Linear฀Technology฀Circuit฀Simulation฀Software\SWCADIII฀contains฀the฀installation฀program฀ swcadiii.exe,฀which฀installs฀a฀program฀called฀LTspice/SwitcherCAD฀III฀on฀your฀computer.฀This฀is฀a฀full-fea-tured฀general-purpose฀electronic฀circuit฀simulation฀program.฀After฀installing฀LTspice,฀I฀recommend฀you฀use฀ the฀automatic฀update฀feature฀to฀download฀the฀most฀recent฀version. You฀may฀also฀wish฀to฀join฀the฀LTspice฀user’s฀group,฀via฀the฀home฀page฀at฀http://groups.yahoo.com/group/ LTspice/. MBasic฀Programs All฀of฀the฀programs฀in฀this฀book฀are฀contained฀in฀this฀directory.฀The฀programs฀are฀organized฀with฀a฀separate฀ directory฀for฀each฀chapter.฀Within฀each฀chapter฀directory฀are฀separate฀directories฀with฀program฀versions฀ compatible฀with฀MBasic฀(and฀MBasic876)฀version฀5.3.0.0฀and฀with฀earlier฀versions฀(5.2.1.1.)฀I฀developed฀ the฀programs฀with฀version฀5.2.1.1฀originally,฀but฀have฀revised฀and฀tested฀each฀for฀compatibility฀with฀version฀ 5.3.0.0.฀฀

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Data฀Sheets฀and฀Application฀Notes

Data฀sheets฀for฀many฀of฀the฀transistors,฀diodes฀and฀integrated฀circuits฀used฀in฀this฀book’s฀circuits฀are฀pro-vided฀in฀the฀directory฀data฀sheets฀and฀application฀notes.฀In฀addition,฀I฀have฀included฀a฀selection฀of฀relevant฀ application฀notes฀and฀other฀material฀from฀key฀semiconductor฀manufacturers.

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C H A P T E R ฀

1

PICs฀“101”

What฀is฀a฀PIC

®

_?฀

PICs฀are฀inexpensive฀one-chip฀computers฀designed฀and฀manufactured฀by฀Microchip฀Technology,฀Inc.฀ The฀acronym฀originally฀stood฀for฀Programmable฀Intelligent฀Computer,฀but฀Microchip’s฀official฀name฀for฀ these฀devices฀is฀now฀PICmicro®฀microcontrollers.฀We฀will฀call฀them฀PICs.฀In฀1977,฀General฀Instruments,฀ Microchip’s฀predecessor,฀developed฀the฀original฀PIC,฀the฀PIC1650.฀The฀PIC1650฀can฀be฀though฀of฀as฀the฀ grandfather฀of฀today’s฀PICs,฀and฀its฀architecture,฀programming฀approach฀and฀other฀features฀directly฀corre-spond฀to฀those฀found฀in฀modern฀PICs.฀Its฀instruction฀set฀and฀register฀arrangement฀mirror฀current฀PICs฀with฀ only฀minor฀differences. General฀Instruments฀sold฀its฀microcontroller฀business฀in฀the฀mid-1980s฀to฀the฀entity฀that฀later฀became฀ Microchip.฀Microchip’s฀current฀product฀line฀includes฀nearly฀200฀PIC฀models฀with฀MBasic฀supporting฀more฀ than฀half.฀Microchip฀has฀sold฀more฀than฀2฀billion฀PICs฀since฀the฀mid-1980s,฀and฀in฀2002฀was฀number฀one฀ worldwide฀in฀8-bit฀microcontroller฀sales,฀based฀on฀number฀of฀units฀shipped. PICs฀are฀microprocessors,฀akin฀to฀the฀ones฀inside฀personal฀computers,฀but฀significantly฀simpler,฀smaller฀ and฀cheaper,฀optimized฀to฀deal฀with฀the฀real฀world—operating฀relays,฀turning฀lamps฀off฀and฀on,฀measuring฀ sensors฀and฀responding฀to฀changed฀readings฀with฀specific฀actions—instead฀of฀running฀word฀processing฀or฀ spread฀sheet฀programs.฀To฀emphasize฀the฀outside฀world฀connection,฀the฀term฀“microcontroller”฀was฀coined฀ to฀distinguish฀it฀from฀a฀“microprocessors.”฀GI฀envisioned฀its฀PIC1650฀as฀a฀means฀to฀replace฀dozens฀of฀ discrete฀logic฀chips฀in฀computers฀using฀its฀CP1600฀microprocessor,฀but฀immediately฀recognized฀the฀power฀ of฀its฀flexible,฀programmable฀design฀serving฀as฀a฀stand-alone฀microcontroller.฀Figure฀1-1฀illustrates฀the฀main฀ elements฀inside฀a฀PIC: •฀ A฀processing฀engine:฀The฀central฀processing฀unit,฀or฀ CPU,฀is฀the฀microcontroller’s฀intelligence.฀It฀performs฀ the฀logical฀and฀arithmetic฀functions฀of฀the฀PIC฀follow-ing฀instructions฀it฀reads฀from฀the฀program฀memory.฀It฀ reads฀from฀and฀writes฀to฀data฀memory฀and฀the฀input/ output฀module. •฀ Program฀memory:฀Holds฀instructions฀for฀the฀CPU.฀The฀ CPU฀reads฀program฀memory฀but฀is฀physically฀prevented฀ in฀most฀model฀PICs฀from฀writing฀to฀program฀memory. •฀ Data฀memory:฀Holds฀memory฀that฀the฀programmer฀ may฀use฀for฀variables.฀The฀CPU฀reads฀from฀and฀writes฀ to฀data฀memory. •฀ Input/output:฀How฀the฀PIC฀communicates฀with฀the฀ world฀outside฀the฀chip;฀for฀example,฀pins฀that฀go฀be-tween฀logical฀0฀and฀logical฀1. _{Figure฀1-1:฀Main฀elements฀of฀a฀PIC.}

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•฀ Peripherals:฀Special฀purpose฀functions฀built฀into฀the฀PIC,฀such฀as฀timers,฀analog-to-digital฀converters฀ and฀pulse฀width฀modulators.฀ If฀you฀are฀familiar฀with฀the฀Intel฀microprocessors฀used฀in฀IBM-compatible฀personal฀computers,฀you฀may฀no-tice฀one฀striking฀difference฀in฀Figure฀1-1;฀the฀program฀memory฀and฀data฀memory฀are฀separate.฀In฀computer฀ techno-speak,฀PICs฀follow฀the฀Harvard฀architecture฀model,฀while฀Intel’s฀microprocessors฀(and฀those฀of฀most฀ other฀manufacturers฀as฀well)฀implement฀von฀Neumann’s฀architecture,฀sharing฀common฀memory฀between฀ program฀and฀data฀as฀necessary.฀Fortunately,฀MBasic฀hides฀the฀details฀of฀this฀difference฀from฀us฀and฀we฀ seldom฀need฀to฀delve฀into฀it.฀One฀place฀this฀difference฀is฀critical,฀though,฀is฀since฀data฀memory฀and฀program฀ memory฀capacities฀are฀separately฀speciﬁed฀in฀PICs,฀both฀must฀be฀sized฀to฀accommodate฀the฀job฀at฀hand.

How฀Do฀I฀Tell฀Them฀Apart?

Microchip฀identiﬁes฀PICs฀with฀a฀multipart฀identiﬁer฀such฀as฀a฀16F877A-E/P: Microchip฀groups฀its฀PIC฀line฀in฀three฀performance฀and฀three฀memory฀type฀categories: Microchip’s฀General฀Purpose฀PIC฀Line฀Name฀(Instruction฀Word฀Length)฀and฀MBasic฀Support

Program฀Memory฀Type Base-Line฀(12-bit) Mid-Range฀(14-bit) High-End฀(16-bit)

EPROM/EEPROM None฀supported฀by฀MBasic 12C,฀12CE,฀16C฀and฀16CE-series฀EPROM฀and฀EEPROM 17C-series฀and฀18C-series.฀ Not฀supported฀by฀MBasic Read-only฀Memory฀(ROM) 16CR-series.฀Not฀supported฀_by฀MBasic Not฀produced฀by฀_Microchip Flash฀(electronically฀erasable) _{Some฀12F-series฀and฀} 16F-series 18F-series.฀Not฀presently฀ supported฀by฀MBasic฀ (See฀Note฀1) 1.฀18F-series฀support฀is฀under฀development฀by฀Basic฀Micro฀and฀will฀be฀included฀in฀a฀future฀MBasic฀release. It฀would฀have฀been฀logical฀for฀Microchip฀to฀use฀the฀series฀identiﬁer฀to฀point฀to฀the฀instruction฀word฀length,฀ but฀it฀missed฀that฀opportunity.฀Thus,฀we฀have฀the฀12C508A,฀a฀12-bit฀device฀and฀the฀12F629,฀a฀14-bit฀device.฀ And,฀we฀have฀the฀16C54C,฀a฀12-bit฀device฀and฀the฀16C554,฀a฀14-bit฀device.฀In฀almost฀all—but฀unfortunately฀ not฀entirely฀all—instances฀a฀16-series฀device฀is฀a฀mid-range฀PIC฀with฀a฀14-bit฀instruction฀word,฀but฀to฀be฀ sure฀we฀must฀consult฀Microchip’s฀reference฀documents.฀ 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 rating applies for the PIC.)

Silicon die layout revision suffix Device type number

Program memory type; C, CR, CE & F Family number; 12, 16, 17 & 18

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The฀instruction฀word฀length฀is฀not฀related฀to฀the฀program฀memory฀size,฀but฀rather฀defines฀how฀many฀unique฀ machine฀code฀instructions฀may฀be฀implemented.฀It฀isn’t฀necessary฀to฀go฀into฀details฀as฀MBasic฀takes฀care฀ of฀this฀for฀us,฀but฀many฀machine฀level฀operands฀include฀an฀8-bit฀literal฀value,฀such฀as฀moving฀a฀defined฀byte฀ value฀(the฀“literal”)฀into฀the฀CPU.฀Since฀the฀8-bit฀literal฀is฀part฀of฀the฀instruction,฀a฀12-bit฀instruction฀word฀ leaves฀only฀four฀bits฀for฀instructions฀containing฀a฀literal,฀resulting฀in฀only฀16฀possible฀unique฀instructions.฀ Moving฀to฀a฀14-bit฀word฀increases฀the฀potential฀instruction฀set฀with฀a฀literal฀to฀64.฀(The฀problem฀of฀limited฀ program฀instruction฀width฀also฀shows฀up฀in฀assembler฀jump฀or฀“go฀to”฀instructions.)฀In฀any฀event,฀since฀ MBasic฀currently฀supports฀only฀midlength฀(14-bit)฀PICs,฀we฀can฀file฀this฀information฀in฀the฀“interesting฀but฀ not฀immediately฀useful”฀category฀in฀the฀back฀of฀our฀minds,฀at฀least฀until฀we฀start฀to฀mix฀assembler฀language฀ routines฀with฀MBasic. Program฀memory฀in฀a฀PIC฀may฀consist฀of฀three฀types: •฀ Read-only:฀Read-only฀memory฀means฀exactly฀that;฀the฀memory฀is฀configured฀at฀the฀time฀of฀manufactur-ing฀to฀contain฀the฀program฀code฀and฀may฀not฀be฀subsequently฀altered,฀something฀economically฀feasible฀ only฀in฀high฀volume฀products.฀MBasic฀does฀not฀support฀PICs฀with฀read-only฀memory.฀ •฀ EPROM฀and฀EEPROM:฀EPROM฀(erasable฀programmable฀read-only฀memory)฀and฀EEPROM฀(electri-cally฀erasable฀programmable฀read-only฀memory)฀memory฀may฀be฀written฀to฀electronically฀through฀the฀ application฀of฀a฀programming฀voltage฀to฀the฀PIC.฀Once฀written,฀EPROM฀memory฀may฀not฀be฀re-written,฀ and฀is฀thus฀becomes฀read-only฀afterwards.฀Microchip฀refers฀to฀these฀devices฀as฀“one฀time฀program-mable”฀or฀OTP฀products.฀EEPROM฀devices,฀however,฀may฀be฀erased฀through฀several฀minutes’฀exposure฀ to฀ultraviolet฀light.฀Electrically,฀Microchip’s฀EPROM฀and฀EEPROM฀chips฀use฀the฀same฀technology,฀ with฀EPROM฀chips฀being฀encapsulated฀in฀opaque฀epoxy.฀EEPROM฀chips฀have฀a฀quartz฀window฀through฀ which฀UV฀light฀may฀reach฀the฀chip฀surface.฀(After฀programming,฀you฀cover฀the฀window฀with฀an฀opaque฀ label฀to฀prevent฀erasure฀through฀ambient฀sunlight฀or฀fluorescent฀light฀exposure.)฀EPROM฀PICs฀may฀be฀ useful฀in฀small฀to฀medium฀volume฀production,฀but฀both฀EPROM฀and฀EEPROM฀devices฀are฀rapidly฀be-ing฀supplanted฀by฀flash฀memory฀PICs. •฀ Flash:฀Flash฀memory฀may฀be฀written฀to฀and฀erased฀electronically฀through฀the฀application฀of฀a฀program-ming฀voltage฀to฀the฀PIC.฀Flash฀memory฀may฀be฀written฀to฀hundreds฀of฀thousands฀of฀times฀without฀error฀ and,฀at฀room฀temperature,฀based฀on฀extrapolated฀life฀testing,฀will฀retain฀data฀for฀100฀years.฀Flash฀is฀ideal฀ for฀developing฀programs฀and฀learning฀MBasic,฀as฀revising฀code฀and฀writing฀the฀revised฀program฀to฀flash฀ requires฀well฀under฀a฀minute฀for฀all฀but฀the฀longest฀programs. Looking฀at฀the฀price฀of฀chips฀of฀similar฀performance฀and฀capacity฀with฀EPROM,฀EEPROM฀and฀flash฀ memory฀types,฀it’s฀easy฀to฀see฀why฀flash฀devices฀are฀taking฀an฀increasing฀share฀of฀the฀market.฀

Memory฀Type Part฀Number Packaging Unit฀Cost฀

EEPROM฀(UV฀erasable) 16CE625/JW Ceramic฀windowed฀18-pin฀DIP฀(CDIP)฀Type฀“JW” $10.64 EPROM฀(one-time฀programming) 16CE625/P Plastic฀18-pin฀DIP฀(PDIP)฀Type฀“P” $4.38

Flash 16F628A Plastic฀18-pin฀DIP฀(PDIP)฀Type฀“P” $3.05 Finally,฀within฀each฀category,฀Microchip฀offers฀standard฀voltage฀(5฀volt฀nominal)฀and฀extended฀voltage฀ (minimum฀voltage฀dependent฀upon฀memory฀type;฀compatible฀with฀5฀volt฀supply;฀some฀with฀built-in฀regula-tor฀for฀operation฀from฀higher฀voltages.)฀PIC’s฀also฀have฀a฀wide฀variety฀of฀memory฀size,฀internal฀peripheral฀ options,฀temperature฀ranges,฀maximum฀operating฀frequency฀and฀packaging.฀These฀variants฀are฀identiﬁed฀ through฀associated฀alphanumeric฀designators.

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Memory฀and฀Voltage฀Designators Memory/Voltage฀ Letter Memory/Voltage฀Type C EPROM CR ROM CE One-time฀programmable฀(EPROM)฀and฀ EEPROM฀(erasable) F Flash HV High฀Voltage฀(15V) LF Low฀Voltage฀Flash LC Low฀Voltage฀One-time฀programmable LCR Low฀Voltage฀ROM Temperature฀Range฀Designators Temperature฀ Letter Temperature฀Range C Commercial฀0°C฀to฀+85°C฀ I ฀Industrial฀-40°C฀to฀+85°C E Extended฀-40°C฀to฀+125°C฀ Partial฀List฀of฀Package฀Designators Package฀Option฀฀Letter Package฀ JW Ceramic฀window฀(EEPROM฀only) P฀ Plastic฀DIP SP/PJ฀for฀28฀pin฀x฀0.3฀(“skinny-dip”) SN,฀OA,฀SM,฀SL,฀OD,฀SO,฀SI SOIC-plastic฀small฀outline;฀surface฀mount PQ QFP-Plastic฀quad฀ﬂatpack฀surface฀mount SS SSOP-plastic฀shrink฀small฀outline฀surface฀ mount ML Chip฀scale฀package ST TSSOP-Plastic฀thin฀shrink฀small฀outline฀ surface฀mount PT TQFP-plastic฀thin฀quad฀ﬂatpack

Which฀One฀Should฀I฀Use?

Let’s฀look฀at฀the฀PICs฀supported฀by฀MBasic.฀ PICS฀Supported฀by฀MBasic ฀฀฀Device Data฀ RAM ADC Program฀

Memory Serial฀I/O Speed Timers

Low฀Voltage฀ Device 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)

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PICS฀Supported฀by฀MBasic

฀฀฀Device

Data฀ RAM ADC

Program฀

Low฀Voltage฀ Device 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 I²C,฀SPI 20 3+WDT PIC16LC62A

PIC16C62B 128 – 2048 I²C,฀SPI 20 3+WDT PIC16LC62B

PIC16C63 192 – 4096 USART,฀I²C,฀SPI 20 3+WDT PIC16LC63

PIC16C63A 192 – 4096 USART,฀I²C,฀SPI 20 3+WDT PIC16LC63A

PIC16C642 176 – 4096 – 20 1+WDT PIC16LC642

PIC16C64A 128 – 2048 I²C,฀SPI 20 3+WDT PIC16LC64A

PIC16C65A 192 – 4096 USART,฀I²C,฀SPI 20 3+WDT PIC16LC65A

PIC16C65B 192 – 4096 USART,฀I²C,฀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 I²C,฀SPI 20 3+WDT PIC16LC717

PIC16C72 128 5 2048 I²C™,฀SPI™ 20 3+WDT PIC16LC72

PIC16C72A 128 5 2048 I²C,฀SPI 20 3+WDT PIC16LC72A

PIC16C73A 192 5 4096 USART,฀I²C,฀SPI 20 3+WDT PIC16LC73A

PIC16C73B 192 5 4096 USART,฀I²C,฀SPI 20 3+WDT PIC16LC73B

PIC16C745 256 5 8192 USB,฀USART 24 3+WDT –

PIC16C74A 192 8 4096 USART,฀I²C,฀SPI 20 3+WDT PIC16LC74A

PIC16C74B 192 8 4096 USART,฀I²C,฀SPI 20 3+WDT PIC16LC74B

PIC16C76 368 5 8192 USART,฀I²C,฀SPI 20 3+WDT PIC16LC76

PIC16C765 256 8 8192 USB,฀USART 24 3+WDT –

PIC16C923 176 – 4096 I²C,฀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

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PICS฀Supported฀by฀MBasic

฀฀฀Device

Data฀ RAM ADC

Program฀

Low฀Voltage฀ Device

PIC16F627 224 – 1024 USART 20 3฀+฀WDT PIC16LF627

PIC16F628 224 – 2048 USART 20 3฀+฀WDT PIC16LF628

PIC16F73 192 5 4096 I²C,฀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 I²C,฀SPI 20 3+WDT PIC16LF872

PIC16F873 192 5 4096 USART,฀I²C,฀SPI 20 3+WDT PIC16LF873

PIC16F873A 192 5 4096 USART,฀I²C,฀SPI 20 3+WDT PIC16LF873A

PIC16F877A 368 8 8192 USART,฀I²C,฀SPI 20 3+WDT PIC16LF877A This฀list฀may฀seem฀bewildering฀at฀first,฀so฀let’s฀go฀through฀the฀table’s฀parameters: Device—This฀is฀simply฀a฀short฀form฀of฀the฀device฀part฀number.฀ Data฀RAM —Data฀RAM฀specifies฀the฀amount฀(in฀bytes)฀of฀random฀access฀memory฀available฀to฀hold฀vari-ables฀in฀your฀MBasic฀program.฀Since฀MBasic฀requires฀some฀RAM฀for฀its฀internal฀use฀not฀all฀the฀Data฀ RAM฀will฀be฀available฀for฀your฀programs.฀RAM฀contents฀are฀lost฀whenever฀the฀power฀is฀removed฀from฀ the฀PIC.฀(Many฀devices฀include฀nonvolatile฀EEPROM฀memory฀as฀well.฀We’ll฀use฀EEPROM฀memory฀in฀ several฀sample฀programs฀in฀later฀chapters.)฀ Program฀Memory—Since฀PICs฀are฀Harvard฀architecture฀devices,฀the฀program฀and฀data฀memory฀are฀ separate.฀The฀Program฀Memory฀column,฀following฀Microchip’s฀documentation,฀identifies฀the฀program฀ memory฀size฀in฀program฀words.฀In฀the฀case฀of฀the฀PICs฀supported฀by฀MBasic,฀the฀word฀length฀is฀14฀ bits.฀The฀MBasic฀compiler,฀however,฀reports฀program฀memory฀use฀in฀8-bit฀bytes,฀as฀shown฀in฀Figure฀ 1-2.฀Should฀you฀wish฀to฀convert฀between฀the฀two,฀the฀compiler฀reports฀one฀14-bit฀word฀as฀1.75฀bytes,฀ and฀conversely,฀1฀byte฀represents฀0.57143฀ 14-bit฀words.฀ ADC—An฀analog-to-digital฀converter฀(ADC)฀ allows฀the฀PIC฀to฀read฀the฀value฀of฀an฀ analog฀voltage฀and฀convert฀it฀to฀a฀numeri-cal฀value.฀Depending฀upon฀the฀model,฀the฀ ADC฀may฀have฀8-bit,฀10-bit฀or฀12-bit฀ resolution.฀Chapter฀11฀shows฀how฀to฀use฀ the฀ADC฀to฀build฀a฀digital฀voltmeter. Figure฀1-2:฀Understanding฀MBasic’s฀memory฀usage฀report.

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Serial฀I/O—Certain฀PICs฀have฀specialized฀hardware฀support฀of฀up฀to฀three฀serial฀standard฀protocols:฀The฀

USART฀ (universal฀synchronous฀asynchronous฀receiver฀transmitter)฀supports฀the฀common฀RS-232-type฀asynchronous฀protocol,฀as฀well฀as฀others;฀I²C฀(inter-integrated฀circuit)฀and฀SPI฀(serial฀peripheral฀ interface)฀are฀both฀primarily฀used฀to฀communicate฀between฀the฀PIC฀and฀other฀integrated฀circuits,฀such฀as฀ add-on฀memory,฀temperature฀sensors,฀serial฀number฀generators฀and฀the฀like.฀MBasic฀however,฀imple-ments฀RS-232-type฀serial฀communications฀(the฀SerIn฀and฀SerOut฀procedures),฀as฀well฀as฀I2_C฀(the฀

I2Cin฀and฀I2Cout฀procedures)฀and฀SPI฀(via฀the฀ShiftIn฀and฀ShiftOut฀procedures)฀in฀software,฀

so฀all฀three฀protocols฀are฀available฀whether฀or฀not฀the฀PIC฀has฀the฀associated฀specialized฀hardware.฀ Indeed,฀in฀some฀respects฀MBasic’s฀software฀solution฀is฀superior,฀as฀it฀permits฀user-defined฀pin฀assign-ments,฀while฀Microchip’s฀hardware฀implementation฀is฀tied฀to฀specific฀pins.฀However,฀MBasic฀supports,฀ through฀the฀HserOut฀and฀HSerIn฀procedures,฀certain฀aspects฀of฀the฀USART฀hardware฀for฀those฀PICs฀ so฀equipped.฀We’ll฀see฀how฀this฀works฀in฀later฀chapters. Speed—The฀maximum฀clock฀speed฀in฀MHz฀that฀the฀PIC฀device฀type฀supports.฀Microchip฀produces฀lower฀ than฀maximum฀speed฀versions฀of฀some฀devices,฀however,฀so฀when฀purchasing฀a฀PIC฀check฀the฀speed฀ suffix.฀Don’t฀buy฀a฀PIC16F876-04/SP฀(4฀MHz฀maximum)฀if฀you฀want฀a฀PIC16F876-10/SP฀(10฀MHz)฀ or฀a฀PIC16F876-20/SP฀(20฀MHz)฀product!฀The฀price฀difference฀between฀the฀slower฀speed฀version฀of฀a฀ device฀type฀and฀the฀maximum฀speed฀version฀is฀usually฀modest. Timers—Timers฀are฀programmable฀internal฀counters.฀Among฀their฀many฀uses฀is฀to฀set฀up฀a฀periodic฀interrupt฀ signal฀that฀causes฀the฀PIC฀to฀perform฀the฀code฀at฀the฀interrupt฀handler.฀The฀watch฀dog฀timer฀(WDT)฀is฀ a฀specialized฀timer฀that฀may฀be฀used฀to฀detect฀and฀take฀action฀upon฀the฀main฀software฀freezing.฀Timers฀ and฀interrupts฀are฀the฀subject฀of฀Chapter฀10.

Low฀Voltage฀Device—Historically,฀PICs฀have฀required฀a฀5-volt฀power฀supply,฀or฀VDD฀voltage.฀With฀the฀trend฀ towards฀lower฀voltage฀logic,฀Microchip฀has฀responded฀with฀low฀voltage฀alternatives฀of฀its฀standard฀PIC฀ lineup.฀The฀low฀voltage฀chips฀are฀identiﬁed฀with฀an฀“L”฀in฀the฀sufﬁx,฀and฀operate฀with฀as฀little฀as฀2.0฀V฀ VDD ,฀although฀slower฀speed฀may฀be฀necessary฀at฀the฀lower฀end฀of฀the฀operating฀voltage฀range.฀Fortu-nately,฀Microchip’s฀low฀voltage฀PICs฀also฀function฀with฀the฀traditional฀5฀V฀supply฀so฀they฀may฀be฀used฀ with฀Basic฀Micro’s฀ICP฀and฀development฀boards.฀

How฀Do฀I฀Pick฀One?

The฀first฀step฀is฀to฀identify฀your฀requirements฀and฀then฀find฀the฀matching฀devices. •฀ How฀many฀I/O฀pins฀do฀you฀need? •฀ How฀much฀RAM฀is฀required?฀Each฀byte฀variable฀declared฀in฀MBasic฀consumes฀one฀byte฀of฀RAM,฀each฀ word฀variable฀two฀bytes฀and฀each฀long,฀four฀bytes. •฀ How฀much฀program฀memory฀is฀required?฀As฀a฀crude฀estimate฀of฀the฀MBasic฀program฀size฀that฀fits฀into฀a฀ particular฀program฀memory฀capacity,฀you฀may฀assume฀400−1300฀words฀for฀library฀functions฀and฀8−20฀ words฀per฀line฀of฀executable฀code,฀depending฀upon฀the฀compiler฀optimization฀choice฀(minimum฀size฀or฀ maximum฀speed),฀the฀mix฀of฀instructions฀used฀and฀the฀length฀of฀the฀program.฀The฀more฀different฀proce-dures฀and฀functions฀used,฀the฀larger฀the฀library฀requirement. •฀ How฀fast฀a฀device฀meets฀your฀speed฀requirements? •฀ Do฀you฀need฀special฀purpose฀functions,฀such฀as฀an฀A/D฀converter,฀a฀USART,฀specific฀timers฀or฀an฀inter-nal฀clock฀oscillator? •฀ How฀does฀the฀cost฀fit฀into฀the฀project฀budget? •฀ Do฀you฀want฀a฀one-time-programmable฀or฀a฀flash฀memory฀device? •฀ Are฀there฀physical฀package฀preferences?฀ •฀ Is฀low-voltage฀operation฀necessary?

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If฀your฀requirements฀are฀uncertain,฀start฀with฀the฀largest,฀most฀fully฀equipped฀PIC฀available,฀and฀reﬁne฀your฀ device฀selection฀later฀as฀you฀are฀further฀along฀the฀process.฀MBasic฀makes฀this฀process฀especially฀easy,฀as฀ the฀same฀MBasic฀code฀runs฀on฀any฀supported฀PIC,฀except,฀of฀course,฀for฀a฀handful฀of฀instructions฀dependent฀ upon฀particular฀hardware฀features.

So,฀Which฀One฀Do฀I฀Really฀Want฀to฀Use?

While฀your฀choice฀of฀PIC฀may฀be฀critical฀if฀you฀are฀planning฀a฀production฀run฀of฀100,000฀products,฀for฀ general฀experimentation฀and฀education,฀I฀prefer฀the฀16F876฀and฀16F877฀devices,฀either฀the฀original฀or฀the฀ ‘876A/‘877A฀versions.฀(For฀most฀purposes,฀there฀isn’t฀a฀significant฀difference฀between฀the฀original฀and฀ A฀suffixed฀‘876฀and฀‘877฀PICs.)฀฀Of฀the฀chips฀currently฀usable฀with฀MBasic,฀these฀four฀devices฀offer฀the฀ maximum฀available฀program฀memory฀(8192฀words),฀the฀maximum฀RAM฀(368฀bytes)฀and฀have฀the฀other฀ “bells฀and฀whistles”฀offered฀by฀Microchip,฀such฀as฀a฀USART฀and฀an฀A/D฀converter.฀For฀a฀particular฀project,฀ the฀choice฀between฀the฀two฀is฀driven฀by฀the฀number฀of฀input/output฀pins฀required,฀with฀the฀‘876฀chips฀having฀ a฀maximum฀of฀22฀possible฀I/O฀pins,฀while฀the฀‘877฀chips฀increase฀to฀33฀possible฀I/O฀pins.฀And,฀of฀course,฀ these฀are฀flash฀memory฀devices฀so฀we฀need฀not฀worry฀about฀UV฀erasers. For฀smaller฀projects,฀the฀16F628฀is฀worthy฀of฀consideration.฀It฀is฀available฀in฀an฀18-pin฀package,฀so฀it฀must฀ be฀used฀with฀Basic฀Micro’s฀0818฀development฀board.฀The฀‘628฀has฀a฀maximum฀I/O฀capacity฀of฀16฀pins,฀and฀ has฀generous฀224฀bytes฀RAM฀and฀2048฀words฀of฀program฀memory.฀It฀does฀not฀have฀an฀ADC. Finally,฀for฀jobs฀that฀require฀a฀tiny฀PIC,฀the฀12F629฀and฀12F675฀devices฀are฀useful.฀Both฀have฀a฀small฀ footprint฀(8-pin฀DIP฀package),฀1024฀words฀of฀program฀memory฀and฀64฀bytes฀of฀RAM.฀The฀12F629฀does฀not฀ have฀an฀A/D฀converter,฀while฀the฀12F675฀does.฀Both฀permit฀up฀to฀six฀of฀their฀eight฀pins฀to฀be฀used฀for฀I/O฀ purposes.฀Either฀chip฀may฀be฀used฀with฀Basic฀Micro’s฀0818฀development฀board.

Basic฀Micro’s฀MBasic876฀Compiler

The฀CD-ROM฀accompanying฀this฀book฀includes฀a฀free฀MBasic876฀compiler฀from฀Basic฀Micro.฀MBa-sic876฀is฀a฀complete,฀100%฀functional฀version฀of฀MBasic,฀limited฀in฀that฀it฀works฀only฀with฀the฀16F876฀and฀ 16F876A฀devices.฀To฀use฀MBasic876฀as฀intended,฀with฀integrated฀debugging฀and฀interactive฀programming,฀ you฀will฀need฀to฀purchase฀Basic฀Micro’s฀in-circuit฀programmer฀(ISP-PRO)฀and฀its฀2840฀Development฀Board.฀ Or,฀if฀you฀are฀willing฀to฀sacriﬁce฀integrated฀debugging฀and฀interactive฀programming—both฀features฀of฀great฀ beneﬁt—you฀may฀use฀MBasic876’s฀output฀HEX฀code฀with฀third-party฀PIC฀programmers.฀We’ll฀look฀at฀the฀ ISP-PRO฀and฀2840฀Development฀Board฀in฀Chapter฀2. You฀should฀not฀regard฀MBasic876’s฀restriction฀to฀the฀‘876฀and฀‘876A฀devices฀as฀a฀serious฀limit,฀as฀these฀ chips฀are฀feature฀and฀performance฀rich฀and,฀in฀fact,฀are฀the฀most฀advanced฀mid-range฀PICs฀available฀in฀a฀ 28-pin฀package.฀With฀only฀a฀handful฀of฀exceptions—where฀more฀I/O฀pins฀are฀required฀than฀are฀available฀ in฀a฀28-pin฀package—every฀circuit฀in฀this฀book฀can฀be฀constructed฀with฀an฀‘876/876A,฀and฀the฀associated฀ programs฀compiled฀by฀MBasic876.฀

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References

[1-1]_{฀฀ Microchip฀provides฀a฀wealth฀of฀PIC฀information,฀available฀for฀free฀downloading,฀on฀its฀Internet฀website,฀} http://www.microchip.com.฀All฀are฀worth฀reading,฀but฀of฀particular฀interest฀to฀beginners฀are฀the฀intro-ductory฀tutorials฀found฀at฀http://www.microchip.com/1010/suppdoc/design/toots/index.htm฀including: •฀ Analog-to-digital฀conversion:฀http://www.microchip.com/download/lit/suppdoc/toots/adc.pdf฀ •฀ Device฀conﬁguration:฀http://www.microchip.com/download/lit/suppdoc/toots/conﬁg.pdf •฀ Power฀considerations:฀http://www.microchip.com/download/lit/suppdoc/toots/power.pdf •฀ On-chip฀Memory:฀http://www.microchip.com/download/lit/suppdoc/toots/ramrom.pdf ฀ Product฀line฀card:฀http://www.microchip.com/1010/pline/picmicro/index.htm฀contains฀a฀detailed฀table฀ identifying฀the฀capabilities฀of฀the฀Microchip฀product฀line. [1-2]฀฀_{A฀complete฀data฀sheet฀for฀most฀PICs฀comprises฀two฀elements;฀(a)฀a฀detailed฀“family”฀reference฀manual฀} and฀(b)฀the฀particular฀device฀data฀sheet.฀MBasic฀supports฀only฀PICs฀from฀Microchip’s฀“midrange”฀fam-ily฀and฀the฀associated฀PICmicro™฀Mid-Range฀MCU฀Family฀Reference฀Manual฀may฀be฀downloaded฀ at฀http://www.microchip.com/download/lit/suppdoc/refernce/midrange/33023a.pdf.฀This฀is฀a฀688-page฀ document,฀in฀almost฀mind฀numbing฀detail,฀but฀nonetheless฀is฀an฀essential฀reference฀to฀a฀complete฀ understanding฀of฀PICs.฀For฀individual฀PIC฀family฀member฀datasheets,฀the฀easiest฀source฀is฀to฀go฀to฀ http://www.microchip.com/1010/pline/picmicro/index.htm฀and฀select฀either฀the฀PIC12฀or฀PIC16฀group฀ and฀from฀that฀link฀then฀select฀the฀individual฀PIC฀device. General฀note฀on฀web฀addresses:฀Manufacturers฀periodically฀reorganize฀their฀websites,฀so฀the฀URLs฀in฀this฀ book฀may฀change฀from฀those฀given฀as฀references.฀The฀documents,฀however,฀may฀be฀easily฀found฀through฀the฀ manufacturer’s฀home฀page฀search฀function,฀or฀through฀a฀general฀search฀engine฀such฀as฀Google.฀

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C H A P T E R ฀

2

MBasic฀Compiler฀and฀

Development฀Boards

The฀Compiler฀Package

A฀Note฀on฀Compiler฀Versions By฀the฀time฀this฀book฀is฀published,฀Basic฀Micro฀will฀have฀released฀an฀updated฀MBasic฀compiler฀(version฀ 5.3.0.0)฀and฀rationalized฀its฀compiler฀family,฀dropping฀its฀“standard”฀version฀compiler,฀making฀the฀former฀ “professional”฀version฀its฀flagship฀PIC฀compiler.฀(If฀you฀are฀still฀using฀version฀5.2.,฀check฀with฀Basic฀Micro฀ for฀upgrade฀information.฀Owners฀of฀MBasic฀Professional฀version฀5.2฀qualify฀for฀a฀free฀upgrade,฀while฀MBa-sic฀Standard฀owners฀qualify฀for฀a฀reduced฀price฀upgrade฀to฀MBasic-Professional.)฀In฀addition,฀Basic฀Micro฀ has฀a฀made฀available฀a฀free฀version฀of฀its฀MBasic฀Professional฀compiler,฀MBasic876฀on฀the฀CD-ROM฀as-sociated฀with฀this฀book.฀MBasic876฀is฀a฀complete,฀100%฀functional฀version฀of฀MBasic฀Professional,฀limited฀ to฀working฀only฀with฀the฀16F876฀and฀16F876A฀devices. All฀programs฀in฀this฀book฀were฀originally฀developed฀and฀tested฀with฀MBasic฀Professional,฀version฀5.2.1.1฀ and฀have฀been฀verified฀with฀a฀pre-release฀version฀of฀5.3.0.0.฀However,฀bug-fixes฀and฀other฀“tweaking”฀to฀the฀ official฀release฀version฀5.3.0.0฀may฀occur฀that฀introduce฀minor฀incompatibilities฀between฀the฀code฀in฀this฀ book฀and฀Basic฀Micro’s฀ultimately฀released฀compiler.฀The฀CD-ROM฀associated฀with฀this฀book฀provides฀both฀ 5.2.1.1-compliant฀and฀5.3.0.0-compilant฀source฀code.฀Chapter฀29฀summarizes฀the฀differences฀between฀ver-sion฀5.3.0.0฀and฀5.2.1.1. Unless฀specifically฀noted,฀this฀book฀assumes฀you฀are฀using฀MBasic฀or฀MBasic876,฀version฀5.3.0.0.฀The฀ printed฀program฀listings฀are฀for฀version฀5.3.0.0. MBasic฀Compiler As฀used฀in฀this฀book,฀Basic฀Micro’s฀MBasic฀compiler฀comprises฀three฀main฀elements: 1.฀ MBasic฀Compiler฀Software—From฀version฀5.3.0.0฀onward,฀Basic฀Micro฀offers฀one฀version฀of฀its฀MBa-sic฀compiler,฀the฀“Professional”฀version.฀MBasic฀runs฀under฀Microsoft’s฀Windows฀operating฀system฀in฀ any฀version฀from฀Windows฀95฀to฀Windows฀XP.฀The฀computer฀requires฀an฀RS-232฀port฀for฀connection฀to฀ the฀ISP-PRO฀programmer฀board.฀A฀second฀RS-232฀port,฀although฀not฀essential,฀is฀useful฀to฀capture฀any฀ serial฀information฀from฀the฀program฀you฀are฀developing.฀If฀your฀computer฀does฀not฀have฀a฀second฀serial฀ port,฀but฀does฀have฀a฀USB฀port,฀you฀may฀wish฀to฀add฀one฀using฀an฀inexpensive฀USB-to-serial฀converter. 2.฀ ISP-PRO฀Programmer—MBasic,฀after฀the฀assembly฀stage฀completes,฀generates฀Microchip-compatible฀ standard฀HEX฀code฀file฀that฀must฀be฀loaded฀into฀the฀PIC.฀Basic฀Micro฀offers฀a฀programmer,฀the฀ISP-PRO,฀well฀integrated฀with฀the฀MBasic฀compiler฀that฀automatically฀loads฀HEX฀code฀file.฀A฀major฀plus฀ of฀Basic฀Micro’s฀ISP-PRO฀is฀real-time฀debugging฀through฀its฀“in-circuit฀debugging”฀or฀ICD฀capabil-ity.฀Although฀it฀would฀be฀possible฀to฀substitute฀a฀third-party฀programmer฀for฀the฀ISP-PRO,฀losing฀both฀

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seamless฀integration฀with฀the฀compiler฀and฀ICD฀ability฀more฀than฀offsets฀any฀cost฀savings.฀The฀ISP-PRO฀communicates฀with฀the฀computer฀running฀MBasic฀via฀an฀RS-232฀cable,฀and฀with฀the฀PIC฀to฀be฀ programmed฀through฀a฀6-wire฀RJ11฀telephone-type฀cable฀for฀Basic฀Micro’s฀development฀and฀prototype฀ boards,฀or฀a฀10-pin฀standardized฀header฀for฀other฀boards. 3.฀ Development฀Board—Basic฀Micro฀offers฀plug฀board฀style฀development฀boards฀and฀solder-in฀prototype฀ boards฀for฀8-฀and฀18-pin฀and฀28-฀and฀40-pin฀PICs.฀The฀experiments฀in฀this฀book฀assume฀the฀user฀has฀ Basic฀Micro’s฀development฀boards.฀These฀boards฀have฀an฀RJ11฀connector฀for฀the฀ISP-PRO฀connection฀ and฀an฀uncommitted฀RS-232฀port฀that฀may฀be฀used฀by฀the฀PIC฀for฀communications฀to฀the฀outside฀world. Note฀on฀Serial฀Ports:฀The฀single฀largest฀source฀of฀trouble฀reported฀in฀calls฀to฀Basic฀Micro’s฀help฀line฀ concerns฀unreliable฀serial฀port฀connections฀with฀laptop฀computers.฀The฀built-in฀serial฀port฀on฀many฀laptop฀ computers฀cannot฀reliably฀operate฀at฀115.2฀kb/s,฀the฀default฀speed฀at฀which฀the฀PC-to-ISP-PRO฀communica-tions฀link฀operates.฀In฀those฀cases,฀Basic฀Micro฀suggests฀using฀an฀inexpensive฀add-on฀USB-to-serial฀adapter฀ to฀substitute฀for฀the฀built-in฀serial฀port฀and฀recommends฀Bafo฀Technologies’฀BF-180฀USB-to-serial฀adapter.฀ A฀slightly฀more฀expensive฀alternative฀that฀I฀have฀had฀reliable฀results฀with฀is฀Belkin’s฀F5U109,฀sold฀as฀a฀ “USB฀PDA฀Adapter,”฀but฀which฀is,฀in฀fact,฀a฀straight฀USB-to-serial฀adapter.฀Many฀other฀USB-to-serial฀adapters฀likely฀will฀ provide฀reliable฀results. In฀addition฀to฀the฀development฀and฀prototype฀boards,฀the฀ISP-PRO฀is฀compatible฀with฀Basic฀Micro’s฀Universal฀Adapter.฀The฀ Universal฀Adapter,฀however,฀does฀not฀contain฀an฀oscillator฀or฀ the฀other฀circuitry฀needed฀to฀actually฀run฀a฀PIC฀program,฀and฀ is฀intended฀for฀programming฀only.฀

BASIC฀and฀Its฀Essentials

This฀book฀is฀not฀intended฀to฀teach฀BASIC฀programming฀from฀the฀ground฀up.฀There฀are฀many฀good฀“BA-SIC฀programming฀for฀the฀beginner”฀books฀and฀we฀assume฀the฀reader฀has฀at฀least฀passing฀familiarity฀with฀ program฀control฀statements,฀mathematic฀procedures฀and฀variable฀assignment฀and฀structure.฀It฀also฀assumes฀ the฀reader฀has฀installed฀the฀MBasic฀compiler฀(either฀the฀full฀version฀or฀MBasic876,฀version฀5.3.0.0฀as฀of฀ the฀date฀of฀writing)฀and฀has฀familiarized฀himself฀with฀the฀first฀80฀pages฀or฀so฀in฀the฀MBasic฀User’s฀Guide.฀ Incidentally,฀because฀MBasic฀is,฀in฀some฀respects,฀a฀return฀to฀the฀early฀days฀of฀micro฀computer฀language฀ implementation,฀I’ve฀found฀20-year฀old฀reference฀documents฀for฀IBM’s฀Personal฀Computer฀BASIC฀benefi-cial฀in฀refreshing฀my฀memory฀on฀some฀of฀the฀finer฀points฀of฀BASIC฀syntax฀or฀procedure฀and฀of฀considerably฀ more฀help฀than฀modern฀books฀detailing,฀for฀example,฀Visual฀Basic.฀A฀visit฀to฀your฀local฀used฀bookstore฀may฀ turn฀up฀useful฀reference฀material.฀I’ve฀provided฀the฀names฀of฀a฀few฀of฀my฀favorite฀long-out-of-print฀BASIC฀ references฀in฀this฀chapter’s฀reference฀section.฀ As฀a฀guide฀to฀finding฀the฀appropriate฀procedure,฀Table฀2-1฀groups฀MBasic’s฀commands฀into฀a฀logical฀฀ classification.฀ Table฀2-1:฀Taxonomy฀of฀MBasic฀functions฀and฀procedures.

Group Procedure Group Procedure

Program฀Flow Repeat/Until While/WEND Do/While For/Next If/Then/Else/EndIf GoTo GoSub/Return Branch Hardware฀Related ADIN ADIN16 Count HPWM SetCapture GetCapture SetCompare Figure฀2-1:฀ISP-PRO฀and฀RJ-11฀jumper฀cable.

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Table฀2-1:฀Taxonomy฀of฀MBasic฀functions฀and฀procedures.

Pin฀Related Button Low PulsIn PulsOut RCTime Reverse Toggle SetPullups INxx Outxx Dirxx Miscellaneous DeBug End Let Nap Sleep Stop EEPROM฀ Data Read ReadDM Write WriteDM Variables Clear Swap I/O I2Cin I2Cout Owin Owout SerDetect SerIn SerOut ShiftIn฀ ShiftOut HSerIn HSerOut Sound฀and฀Sound฀Related DTMFOut DTMFOut2 FreqOut PWM Sound Sound2 LCD LCDWrite฀ LCDRead LCDInit Data฀Table LookDown LookUp Timing Pause PauseUs PauseClk Memory฀Related Peek Poke

Random฀Generator Random Program฀Memory ReadPM

WritePM On฀Reset OnPOR OnBOR OnMOR Explicit฀External฀ Device฀Support Servo SPMotor Xin Xout Interrupts Enable Disable OnInterrupt SetExtInt SetTmr0 SetTmr1 SetTmr2 IsrASM GetTimer1 Assembler ASM฀{} ISRASM

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Table฀2-1:฀Taxonomy฀of฀MBasic฀functions฀and฀procedures.

Command฀Modiﬁers Dec Hex Bin Str Sdec Shex Sbin Ihex Ibin ISHex ISBin REP Real WaitStr Wait Skip Math฀Operators฀ and Functions + -* LowMult HighMult FractionalMult / // ABS SIN COS DCD SQR BIN2BCD BCD2BIN Max Min Dig Rev Bitwise฀Operators ! & | ^ >> << Comparison฀Operators = <> < > <= >= Logical฀Operators And Or Xor Not฀And Not฀Or Not฀Xor Floating฀Point฀Conversion ToInt ToFloat FloatTable

Development฀Boards

Basic฀Micro฀offers฀two฀breadboard฀style฀development฀boards;฀models฀0818฀for฀8-฀and฀18-pin฀DIP฀PICs,฀ (Figure฀2-2),฀and฀the฀2840฀for฀28฀and฀40-pin฀DIP฀PICs,฀(Figure฀2-3).฀Both฀boards฀have฀a฀small฀solderless฀ plug-in฀area฀for฀additional฀components฀and฀are฀full฀assembled฀with฀surface฀mount฀components.฀Sockets฀are฀ installed฀for฀the฀PICs.฀An฀expanded฀development฀board,฀is฀under฀development฀and฀may฀be฀available฀by฀the฀ time฀this฀book฀is฀published.

Figure฀ 2-2:฀ Basic฀ Micro’s฀ 0818฀ development฀฀ board.

Figure฀ 2-3:฀ Basic฀ Micro’s฀ 2840฀ development฀ board.

Additionally,฀Basic฀Micro฀offers฀corresponding฀semi-permanent฀prototype฀boards,฀models฀08/18,฀Figure฀ 2-4฀and฀28/40,฀Figure฀2-5฀differing฀from฀the฀development฀boards฀in฀that฀additional฀components฀are฀to฀be฀ soldered฀in฀rather฀than฀plugged฀into฀a฀solderless฀breadboard.฀These฀are฀sold฀as฀bare฀boards,฀but฀Basic฀Micro฀ also฀offers฀an฀inexpensive฀complete฀parts฀kit.฀The฀prototype฀boards฀use฀through-hole฀components.

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All฀four฀boards฀permit฀in-circuit฀programming—that฀is,฀the฀ PIC฀may฀be฀programmed฀without฀removing฀it฀from฀your฀ board,฀or฀disconnecting฀its฀pins฀from฀whatever฀you฀may฀have฀ connected฀to฀them.฀Figure฀2-6,฀a฀simplified฀block฀diagram฀of฀ the฀28/40฀prototype฀board,฀shows฀how฀this฀is฀possible.฀Three฀ of฀the฀pins฀required฀for฀programming,฀RB4,฀RB6฀and฀RB7,฀ are฀switched฀through฀a฀74HC4053฀analog฀multiplexer/de-multiplexer฀between฀their฀normal฀connection฀to฀the฀PIC฀pin฀ header฀and฀the฀RJ11฀socket฀that฀connects฀to฀the฀ISP-PRO฀ programmer.฀For฀our฀purpose,฀the฀74HC4053฀can฀be฀regarded฀ as฀an฀electronic฀three-pole฀double฀throw฀switch,฀controlled฀by฀ the฀ISP-PRO.฀The฀MCLR฀(master฀clear)฀pin฀is฀the฀fourth฀con-nection฀required฀for฀programming฀and฀is฀directly฀connected฀ to฀the฀RJ11฀programming฀socket. The฀0818฀and฀08/18฀boards฀follow฀a฀similar฀design,฀but฀with฀ extra฀configuration฀jumpers฀necessitated฀by฀the฀multiple฀func-tions฀Microchip฀assigned฀to฀certain฀pins฀of฀PICs฀produced฀in฀8฀ and฀18-pin฀packages.฀The฀0818฀and฀08/18฀data฀sheets฀should฀ be฀consulted฀before฀programming฀these฀small฀PICs. All฀four฀boards฀bring฀the฀various฀PIC฀pins฀to฀logically฀ labeled฀headers;฀for฀example,฀A0,฀A1,฀so฀you฀don’t฀have฀to฀continually฀cross-reference฀physical฀pin฀numbers฀ with฀their฀logical฀assignments.฀ In฀working฀with฀Basic฀Micro’s฀development฀boards฀and฀ISP-PRO฀programmer฀watch฀out฀for฀the฀following: •฀ These฀are฀sold฀as฀bare฀boards,฀with฀unprotected฀traces฀on฀the฀bottom.฀Don’t฀put฀them฀down฀on฀conductive฀ surfaces฀or฀the฀board฀may฀be฀damaged฀and฀watch฀for฀stray฀wires฀or฀component฀leads฀as฀well.฀(I฀watched฀ my฀ISP-PRO฀board฀be฀dragged฀by฀its฀serial฀cable฀across฀the฀metal฀edge฀on฀the฀table฀and฀looked฀on฀help-lessly฀as฀sparks฀flew.฀Needless฀to฀say,฀the฀ISP-PRO฀didn’t฀work฀after฀that.)฀It฀helps฀to฀add฀small฀stick-on฀ rubber฀feet฀to฀the฀bottom฀of฀all฀boards. •฀ It฀is฀possible฀to฀damage฀the฀74HC4053฀electronic฀switch,฀as฀is฀rated฀at฀a฀maximum฀switched฀current฀of฀25฀ mA.฀The฀most฀likely฀damage฀scenario฀comes฀from฀forcing฀the฀PIC฀to฀sink฀excessive฀current.฀Additionally,฀ unlike฀a฀mechanical฀relay,฀the฀74HC4053฀introduces฀approximately฀80฀to฀100฀ohms฀of฀series฀resistance. Another฀difficulty฀beginners฀often฀have฀is฀confusing฀VDD฀and฀VSS฀when฀wiring฀circuits.฀VSS฀is฀ground฀in฀Basic฀ Micro’s฀development฀boards.฀VDD฀is฀the฀supply฀voltage฀and฀is฀+5฀volts฀in฀the฀development฀boards.฀Thus฀a฀ schematic฀reference฀to฀+5฀V฀is฀the฀same฀as฀VDD฀and฀a฀reference฀to฀ground฀corresponds฀to฀VSS .฀(This฀terminol-ogy฀comes฀from฀VDD฀as฀the฀“drain”฀voltage฀and฀VSS฀as฀the฀“source”฀voltage฀for฀a฀field฀effect฀transistor,฀the฀ basic฀building฀block฀of฀PICs.)฀

Figure฀ 2-4:฀ Basic฀ Micro’s฀ 08/18฀ prototype฀ board.

Figure฀ 2-5:฀ Basic฀ Micro’s฀ 28/40฀ prototype฀ board.

Figure฀ 2-6:฀ Simplified฀ block฀ diagram฀ of฀ 28/40฀ prototype฀board.

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Programming฀Style

Every฀program฀printed฀in฀the฀text฀is฀also฀provided฀as฀a฀file฀in฀the฀accompanying฀CD-ROM฀with฀two฀versions฀ supplied—the฀originally฀developed฀programs฀compatible฀with฀MBasic฀version฀5.2.1.1.฀and฀a฀revised฀ver-sion฀compatible฀with฀5.3.0.0.฀There฀may฀be฀differences฀between฀the฀printed฀program฀and฀the฀CD-ROM฀for฀ several฀reasons: •฀ The฀CD-ROM฀is฀quicker฀to฀update฀and฀may฀have฀a฀later฀or฀corrected฀version฀of฀the฀text฀program. •฀ Page฀width฀and฀overall฀length฀restrictions฀make฀it฀necessary฀to฀limit฀the฀comments฀and฀blank฀spaces฀ used฀on฀the฀printed฀page.฀The฀data฀files฀have฀no฀similar฀restriction฀and฀hence฀may฀have฀additional฀com-ments฀and฀may฀be฀formatted฀for฀greater฀readability.฀(Although฀not฀documented฀in฀the฀User’s฀Guide,฀ MBasic฀uses฀the฀vertical฀bar฀“฀|฀”฀as฀a฀continuation฀symbol,฀thus฀allowing฀one฀logical฀line฀of฀BASIC฀ code฀to฀be฀split฀over฀two฀or฀more฀physical฀lines.) Standard฀Program฀Layout As฀an฀aid฀in฀readability฀and฀maintainability,฀I฀like฀to฀follow฀a฀standard฀layout฀when฀programming,฀as฀exem-plified฀in฀the฀following฀template:฀ ;Program฀Sample.Bas฀–฀File฀name฀ ;Version฀1.00 ;14฀September฀2003฀–฀original฀version ; ;Constants ;---Define฀constants฀here ;Variables ;---Declare฀variables฀here ;Initialization ;---Initialization฀code฀here฀–฀this฀code฀is฀executed฀only฀once Main ;---Main฀code฀segment฀here If฀something฀GoSub฀Sub1 If฀something฀else฀GoSub฀Sub2 If฀something฀totally฀different฀happens฀GoSub฀Sub3 GoTo฀Main฀;if฀appropriate฀to฀have฀a฀continuous฀loop฀฀ Sub1 ;---฀ Subroutine฀code฀here Return Sub2 ;---฀ Subroutine฀code฀here Return Sub3 ;---฀ Subroutine฀code฀here ฀ Includes฀GoSub฀SubSub1 Return SubSub1 ;---฀ Subroutine฀code฀goes฀here Return End