毕业设计外文翻译89C51单片机.docx

毕业设计外文翻译89C51单片机.docx

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毕业设计外文翻译89C51单片机

毕业设计外文翻译--89C51单片机

TheDescriptionofAT89S51

1GeneralDescription

TheAT89S51isalow-power,high-performanceCMOS8-bitmicrocontrollerwith4KbytesofIn-SystemProgrammableFlashmemory.ThedeviceismanufacturedusingAtmel’shigh-densitynonvolatilememorytechnologyandiscompatiblewiththeindustry-standard80C51instructionsetandpinout.Theon-chipFlashallowstheprogrammemorytobereprogrammedin-systemorbyaconventionalnonvolatilememoryprogrammer.Bycombiningaversatile8-bitCPUwithIn-SystemProgrammableFlashonamonolithicchip,theAtmelAT89S51isapowerfulmicrocontrollerwhichprovidesahighly-flexibleandcost-effectivesolutiontomanyembeddedcontrolapplications.

TheAT89S51providesthefollowingstandardfeatures:

4KbytesofFlash,128bytesofRAM,32I/Olines,Watchdogtimer,twodatapointers,two16-bittimer/counters,afive-vectortwo-levelinterruptarchitecture,afullduplexserialport,on-chiposcillator,andclockcircuitry.Inaddition,theAT89S51isdesignedwithstaticlogicforoperationdowntozerofrequencyandsupportstwosoftwareselectablepowersavingmodes.

TheIdleModestopstheCPUwhileallowingtheRAM,timer/counters,serialport,andinterruptsystemtocontinuefunctioning.ThePower-downmodesavestheRAMcontentsbutfreezestheoscillator,disablingallotherchipfunctionsuntilthenextexternalinterruptorhardwarereset.

2Ports

Port0isan8-bitopendrainbi-directionalI/Oport.Asanoutputport,eachpincansinkeightTTLinputs.When1sarewrittentoport0pins,thepinscanbeusedashigh-impedanceinputs.Port0canalsobeconfiguredtobethemultiplexedlow-orderaddress/databusduringaccessestoexternalprogramanddatamemory.Inthismode,P0hasinternalpull-ups.Port0alsoreceivesthecodebytesduringFlashprogrammingandoutputsthecodebytesduringprogramverification.Externalpull-upsarerequiredduringprogramverification.

Port1isan8-bitbi-directionalI/Oportwithinternalpull-ups.ThePort1outputbufferscansink/sourcefourTTLinputs.When1sarewrittentoPort1pins,theyarepulledhighbytheinternalpull-upsandcanbeusedasinputs.Asinputs,Port1pinsthatareexternallybeingpulledlowwillsourcecurrent（IIL）becauseoftheinternalpull-ups.

Port1alsoreceivesthelow-orderaddressbytesduringFlashprogrammingandverification.

PortPin

AlternateFunctions

P1.5

MOSI（usedforIn-SystemProgramming）

P1.6

MOSO（usedforIn-SystemProgramming）

P1.7

SCK（usedforIn-SystemProgramming）

Port2isan8-bitbi-directionalI/Oportwithinternalpull-ups.ThePort2outputbufferscansink/sourcefourTTLinputs.When1sarewrittentoPort2pins,theyarepulledhighbytheinternalpull-upsandcanbeusedasinputs.Asinputs,Port2pinsthatareexternallybeingpulledlowwillsourcecurrent（IIL）becauseoftheinternalpull-ups.Port2emitsthehigh-orderaddressbyteduringfetchesfromexternalprogrammemoryandduringaccessestoexternaldatamemorythatuse16-bitaddresses（MOVX@DPTR）.Inthisapplication,Port2usesstronginternalpull-upswhenemitting1s.Duringaccessestoexternaldatamemorythatuse8-bitaddresses（MOVX@RI）,Port2emitsthecontentsoftheP2SpecialFunctionRegister.Port2alsoreceivesthehigh-orderaddressbitsandsomecontrolsignalsduringFlashprogrammingandverification.

Port3isan8-bitbi-directionalI/Oportwithinternalpull-ups.ThePort3outputbufferscansink/sourcefourTTLinputs.When1sarewrittentoPort3pins,theyarepulledhighbytheinternalpull-upsandcanbeusedasinputs.Asinputs,Port3pinsthatareexternallybeingpulledlowwillsourcecurrent（IIL）becauseofthepull-ups.Port3receivessomecontrolsignalsforFlashprogrammingandverification.Port3alsoservesthefunctionsofvariousspecialfeaturesoftheAT89S51,asshowninthefollowingtable.

PortPin

AlternateFunctions

P3.0

RXD（serialinputport）

P3.1

TXD（serialoutputport）

P3.2

INT0（externalinterrupt0）

P3.3

INT1（externalinterrupt1）

P3.4

T0（timer0externalinput）

P3.5

T1（timer1externalinput）

P3.6

WR（externaldatamemorywritestrobe）

P3.7

RD（externaldatamemoryreadstrobe）

3MemoryOrganization

MCS-51deviceshaveaseparateaddressspaceforProgramandDataMemory.Upto64KbyteseachofexternalProgramandDataMemorycanbeaddressed.

3.1ProgramMemory

IftheEApinisconnectedtoGND,allprogramfetchesaredirectedtoexternalmemory.OntheAT89S51,ifEAisconnectedtoVCC,programfetchestoaddresses0000HthroughFFFHaredirectedtointernalmemoryandfetchestoaddresses1000HthroughFFFFHaredirectedtoexternalmemory.

3.2DataMemory

TheAT89S51implements128bytesofon-chipRAM.The128bytesareaccessibleviadirectandindirectaddressingmodes.Stackoperationsareexamplesofindirectaddressing,sothe128bytesofdataRAMareavailableasstackspace.

4WatchdogTimer（One-timeEnabledwithReset-out）

TheWDTisintendedasarecoverymethodinsituationswheretheCPUmaybesubjectedtosoftwareupsets.TheWDTconsistsofa14-bitcounterandtheWatchdogTimerReset（WDTRST）SFR.TheWDTisdefaultedtodisablefromexitingreset.ToenabletheWDT,ausermustwrite01EHand0E1HinsequencetotheWDTRSTregister（SFRlocation0A6H）.WhentheWDTisenabled,itwillincrementeverymachinecyclewhiletheoscillatorisrunning.TheWDTtimeoutperiodisdependentontheexternalclockfrequency.ThereisnowaytodisabletheWDTexceptthroughreset（eitherhardwareresetorWDToverflowreset）.WhenWDToverflows,itwilldriveanoutputRESETHIGHpulseattheRSTpin.

4.1UsingtheWDT

ToenabletheWDT,ausermustwrite01EHand0E1HinsequencetotheWDTRSTregister（SFRlocation0A6H）.WhentheWDTisenabled,theuserneedstoserviceitbywriting01EHand0E1HtoWDTRSTtoavoidaWDToverflow.The14-bitcounteroverflowswhenitreaches16383（3FFFH）,andthiswillresetthedevice.WhentheWDTisenabled,itwillincrementeverymachinecyclewhiletheoscillatorisrunning.ThismeanstheusermustresettheWDTatleastevery16383machinecycles.ToresettheWDTtheusermustwrite01EHand0E1HtoWDTRST.WDTRSTisawrite-onlyregister.TheWDTcountercannotbereadorwritten.WhenWDToverflows,itwillgenerateanoutputRESETpulseattheRSTpin.TheRESETpulsedurationis98xTOSC,whereTOSC=1/FOSC.TomakethebestuseoftheWDT,itshouldbeservicedinthosesectionsofcodethatwillperiodicallybeexecutedwithinthetimerequiredtopreventaWDTreset.

4.2WDTDURINGPower-downandIdle

InPower-downmodetheoscillatorstops,whichmeanstheWDTalsostops.WhileinPower-downmode,theuserdoesnotneedtoservicetheWDT.TherearetwomethodsofexitingPower-downmode:

byahardwareresetorviaalevel-activatedexternalinterrupt,whichisenabledpriortoenteringPower-downmode.WhenPower-downisexitedwithhardwarereset,servicingtheWDTshouldoccurasitnormallydoeswhenevertheAT89S51isreset.ExitingPower-downwithaninterruptissignificantlydifferent.Theinterruptisheldlowlongenoughfortheoscillatortostabilize.Whentheinterruptisbroughthigh,theinterruptisserviced.TopreventtheWDTfromresettingthedevicewhiletheinterruptpinisheldlow,theWDTisnotstarteduntiltheinterruptispulledhigh.ItissuggestedthattheWDTberesetduringtheinterruptservicefortheinterruptusedtoexitPower-downmode.ToensurethattheWDTdoesnotoverflowwithinafewstatesofexitingPower-down,itisbesttoresettheWDTjustbeforeenteringPower-downmode.BeforegoingintotheIDLEmode,theWDIDLEbitinSFRAUXRisusedtodeterminewhethertheWDTcontinuestocountifenabled.TheWDTkeepscountingduringIDLE（WDIDLEbit=0）asthedefaultstate.TopreventtheWDTfromresettingtheAT89S51whileinIDLEmode,theusershouldalwayssetupatimerthatwillperiodicallyexitIDLE,servicetheWDT,andreenterIDLEmode.

WithWDIDLEbitenabled,theWDTwillstoptocountinIDLEmodeandresumesthecountuponexitfromIDLE.

5.Interrupts

TheAT89S51hasatotaloffiveinterruptvectors:

twoexternalinterrupts（INT0andINT1）,twotimerinterrupts（Timers0and1）,andtheserialportinterrupt.TheseinterruptsareallshowninFigure6-1.EachoftheseinterruptsourcescanbeindividuallyenabledordisabledbysettingorclearingabitinSpecialFunctionRegisterIE.IEalsocontainsaglobaldisablebit,EA,whichdisablesallinterruptsatonce.

6OscillatorCharacteristics

XTAL1andXTAL2aretheinputandoutput,respectively,ofaninvertingamplifierthatcanbeconfiguredforuseasanon-chiposcillator,asshowninFigure7-1.Eitheraquartzcrystalorceramicresonatormaybeused.Todrivethedevicefromanexternalclocksource,XTAL2shouldbeleftunconnectedwhileXTAL1isdriven,asshowninFigure7-2.Therearenorequirementsonthedutycycleoftheexternalclocksignal,sincetheinputtotheinternalclockingcircuitryisthroughadivide-by-twoflip-flop,butminimumandmaximumvoltagehighandlowtimespecificationsmustbeobserved.

7IdleMode

Inidlemode,theCPUputsitselftosleepwhilealltheon-chipperipheralsremainactive.Themodeisinvokedbysoftware.Thecontentoftheon-chipRAMandallthespecialfunctionregistersremainunchangedduringthismode.Theidlemodecanbeterminatedbyanyenabledinterruptorbyahardwarereset.

Notethatwhenidlemodeisterminatedbyahardwarereset,thedevicenormallyresumespro-gramexecutionfromwhereitleftoff,uptotwomachinecyclesbeforetheinternalresetalgorithmtakescontrol.On-chiphardwareinhibitsaccesstointe