example square wave - mechanical engineering例方波-机械工程

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1、EMCH367FundamentalsofMicrocontrollersExampleSQUAREWAVEEXAMPLESQUAREWAVEOBJECTIVEThisexamplehasthefollowingobjectives:·Reviewtheuseparallelports·IllustratethegenerationofasquarewaveusingPortBoutputandawaitingsequence·Demonstratetheuseofasubroutinetoshortenthelengthofaprog

2、ram·ExaminetherelationbetweendisplayedsimulationtimeandclockcyclesinTHRSim11simulatorFigure1Squarewaveschematicsshowingthehalf-waveduration,Dt,andthelow(L)andhigh(H)states.PROGRAMSThisexampleusestwoprogramsthatproducethesameoutput–thegenerationofasquarewaveofprogrammable

3、wavelength.ThewavelengthisprogrammedusingthevariableDELAY.Thesquare-waveelectricalsignalisoutputthroughsecondpinofPortB,i.e.,pinPB1.Thedifferencebetweenthefirstandsecondprogramconsistintheuseofasubroutine.Theuseofasubroutinecompressesthecodeandshortensthetotallengthofthe

4、program.Dr.VictorGiurgiutiuPage142021/6/21EMCH367FundamentalsofMicrocontrollersExampleSQUAREWAVEProgramsq_wav1InstructionsDefinevariableDELAYat$0000LoadREGBASinreg.XSendlowsignalLoad%00000000inaccAStoreaccAinPortBLoadDELAYintoaccBDecreaseaccBinaloopuntilzeroSendhighsigna

5、lLoad%00000010inaccAStoreaccAinPortBLoadDELAYintoaccBDecreaseaccBinaloopuntilzeroBranchbackto(iii)SWIFlowchartCodeDELAYRMB1*StartmainprogramORGPROGRAMSTARTLDX#REGBAS*Begintypingyourcode*SendlowsignalBEGINLDAA#%00000000STAAPORTB,XLDABDELAYLABEL1SUBB#1BHILABEL1*Sendhighsig

6、nalLDAA#%00000010STAAPORTB,XLDABDELAYLABEL2SUBB#1BHILABEL2BRABEGINSWIFLOWCHARTANDCODETheprogramflowchartisshowtotherightoftheprograminstructions.Notethe‘sendlowsignal’and‘sendhighsignal’blocks.Alsonotethetwowaitblocks,onesendingthelowsignal,theotheraftersendingthehighsig

7、nal.Thewaitblocksarenotdetailed,sincetheyhavebeencoveredinapreviousexampleandcanbedirectlyclonedfromthere(the‘codereuse’concept).Theessentialcodeforthisprogramisshowntotheleftoftheflowchart.ThefileSq_wav1.asmistheresultofincorporatingthiscodeinthestandardtemplate.EXECUTI

8、ONOpenTHRSim11.ClosetheCommandswindow.Openmemorylist,portregisters,andTHRSim11IObox.OpenandassembleSq_w