MISCELLAI{EOUS EXERCISES in Software

Generation PDF417 in Software MISCELLAI{EOUS EXERCISES

Theseexercisesate designedto challengeyour programming ability Again, you will need accessto ihe datasheet the LC Display lbr

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

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

and in Timedlwill be covered moredetailasa protollpicaltimer,anddiscussion exam plesfor the useofTimerl andTirner2will be providcd thanwhatwe is to The useoftimers internal microprocessorsa bit morecomplicated required before amount ofsetup thercis a considerable havebeendoingso far because for up rnd alsobecause options setting the timersareextenthe the limercan be used, but sivcWe will coverlhe timersone at a time in an intoductory manner, be warned that there is an entirc man\al (Plcnicro Micl RangeMCU Faniry Rekrence Manual Incnothingbut timers' liom MicrochipTechnology thatcovers lDS33023l)available be herewill, olnccessity, rudimentary so our coverage how timershasto do with understanding to tum themON andOFF Understanding in bits andhow to readandsetthe various andbytesrhatrelatcto themEssentially, ihe bit typicaltimer applicatiot,you turn a tiner ON by turningon its enable The timer an bit, thencountsa certainnumberofclock cyclesand setsall interrupt thus causing progmm respondsto the intenupt by execntinga specifc inkrrupt han' intemrpt Youlll dling routine ard iJ|'et\clearingthe intenupt bit ]lhe progra"nthen relurns to wherever have The it was whenthe inteffuptoccurred pre/postscalars to do with modifyingthe placeThe hardpail is findingou! which bit does time it takesfor an inteffuptto take chaptcron the what and where it is located, so readingand understarding the datasheet ihis Thereis no escaping horrorl tiner you areusingis imperative include: cventsThese Timersallowthemicrcontmller to cr aFandrcactto chronological : I I I ! ! Timing events of The creation clockslbr variouspurposes Generatingtimed interrupts Controling PWM generation to Wakingthe PIC from its sleepmodeat jntervals do work (andbackto sleep) timer use Special oflhe watchdog

timer,which Thereis alsothewatchdog timers thrceinternrl The PIC 16F877Ahas afterthe standard timers is discussed prescalar the It's with an optioDal timer/counter t Timero An 8-bit free-running of the timersto use simplest It ! Timerl A 16 bi! tiner that canbe usedasa timer or asa counter- is the only I6-bit mostcomplicaled thetimers of is as timerthatcanbe used a counterIt alsothe and and r Timer2 An 8-bit timer with a prescalar postscalar cannotbe usedas a There n,JInpullrnefor rhi lim(r i counrer Eachtimer hasa timer control registerthat selsthe optionsandpropertiesthat the timer that features givc it will exhibitAll thetime$ aresimilarandeachof themhasspecial you for propertics is imperative referto your datasheet the PIC l6F877Aas It special what ihe PIC Onceyou startto understand you experiment with the timer functions in will startto cometogether yourmind it are designers up to wilh lhe timerfunctions