单片机AT89C52简要说明.docx

单片机AT89C52简要说明.docx

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单片机AT89C52简要说明

附录A英文原文

MicrocomputerAT89C52SynopticElucidation

ThemicrocomputerAT89C52providesthefollowingstandardfeatures:

8KbytesofFlash,256bytesofRAM,32I/Olines,three16-bittimer/counters,asix-vectortwo-levelinterruptarchitecture,afullduplexserialport,on-chiposcillator,andclockcircuitry.Inaddition,theAT89C52isdesignedwithstaticlogicforoperationdowntozerofrequencyandsupportstwosoftwareselectablepowersavingmodes.TheIdleModestopstheCPUwhileallowingtheRAM,timer/counters,serialport,andinterruptsystemtocontinuefunctioning.ThePowerDownModesavestheRAMcontentsbutfreezestheoscillator,disablingallotherchipfunctionsuntilthenexthardwarereset,forthefigure1.

PinDescription

VCC:

Supplyvoltage.

GND:

Ground.

Port0:

Port0isan8-bitopendrainbidirectionalI/Oport.Asanoutputport,eachpincansinkeightTTLinputs.When1sarewrittentoport0pins,thepinscanbeusedashighimpedanceinputs.Port0canalsobeconfiguredtobethemultiplexedloworderaddress/databusduringaccessestoexternalprogramanddatamemory.Inthismode,P0hasinternalpullups.Port0alsoreceivesthecodebytesduringFlashprogrammingandoutputsthecodebytesduringprogramverification.Externalpull-upsarerequiredduringprogramverification.

Port1:

Port1isan8-bitbidirectionalI/Oportwithinternalpullups.ThePort1outputbufferscansink/sourcefourTTLinputs.When1sarewrittentoPort1pins,theyarepulledhighbytheinternalpull-upsandcanbeusedasinputs.Asinputs,Port1pinsthatareexternallybeingpulledlowwillsourcecurrent（IIL）becauseoftheinternalpull-ups.Inaddition,P1.0andP1.1canbeconfiguredtobethetimer/counter2externalcountinput（P1.0/T2）andthetimer/

counter2triggerinput（P1.1/T2EX）,respectively,asshowninthefollowingtable.Port1alsoreceivesthelow-orderaddressbytesduringFlashprogrammingandverification.

Port2:

Port2isan8-bitbidirectionalI/Oportwithinternalpullups.ThePort2outputbufferscansink/sourcefourTTLinputs.When1sarewrittentoPort2pins,theyarepulledhighbytheinternalpull-upsandcanbeusedasinputs.Asinputs,Port2pinsthatareexternallybeingpulledlowwillsourcecurrent（IIL）becauseoftheinternalpull-ups.Port2emitsthehighorderaddressbyteduringfetchesfromexternalprogrammemoryandduringaccessestoexternaldatamemorythatuse16-bitaddresses（MOVX@DPTR）.Inthisapplication,Port2usesstronginternalpull-upswhenemitting1s.Duringaccessestoexternaldatamemorythatuse8-bitaddresses（MOVX@RI）,Port2emitsthecontentsoftheP2SpecialFunctionRegister.Port2alsoreceivesthehigh-orderaddressbitsandsomecontrolsignalsduringFlashprogrammingandverification.

Port3:

Port3isan8-bitbidirectionalI/Oportwithinternalpullups.ThePort3outputbufferscansink/sourcefourTTLinputs.When1sarewrittentoPort3pins,theyarepulledhighbytheinternalpull-upsandcanbeusedasinputs.Asinputs,Port3pinsthatareexternallybeingpulledlowwillsourcecurrent（IIL）becauseofthepullups.Port3alsoservesthefunctionsofvariousspecialfeaturesoftheAT89C51,asshowninthefollowingtable.Port3alsoreceivessomecontrolsignalsforFlashprogrammingandverification.

RST:

Resetinput.Ahighonthispinfortwomachinecycleswhiletheoscillatorisrunningresetsthedevice.

ALE/PROG:

AddressLatchEnableisanoutputpulseforlatchingthelowbyteoftheaddressduringaccessestoexternalmemory.Thispinisalsotheprogrampulseinput（PROG）duringFlashprogramming.Innormaloperation,ALEisemittedataconstantrateof1/6theoscillatorfrequencyandmaybeusedforexternaltimingorclockingpurposes.Note,however,thatoneALEpulseisskippedduringeachaccesstoexternaldatamemory.Ifdesired,ALEoperationcanbedisabledbysettingbit0ofSFRlocation8EH.Withthebitset,ALEisactiveonlyduringaMOVXorMOVCinstruction.Other-wise,thepinisweaklypulledhigh.SettingtheALE-disablebithasnoeffectifthemicrocontrollerisinexternalexecutionmode.

PSEN:

ProgramStoreEnableisthereadstrobetoexternalprogrammemory.WhentheAT89C52isexecutingcodefromexternalprogrammemory,PSENisactivatedtwiceeachmachinecycle,exceptthattwoPSENactivationsareskippedduringeachaccesstoexternaldatamemory.

EA/VPP:

ExternalAccessEnable.EAmustbestrappedtoGNDinordertoenablethe

图A.1AT89C52方框图

devicetofetchcodefromexternalprogrammemorylocationsstartingat0000HuptoFFFFH.Note,however,thatiflockbit1isprogrammed,EAwillbeinternallylatchedonreset.EAshouldbestrappedtoVCCforinternalprogramexecutions.Thispinalsoreceivesthe12-voltprogrammingenablevoltage（VPP）duringFlashprogrammingwhen12-voltprogrammingisselected.

XTAL1:

Inputtotheinvertingoscillatoramplifierandinputtotheinternalclockoperatingcircuit.

XTAL2:

Outputfromtheinvertingoscillatoramplifier.

SpecialFunctionRegisters：

Notalloftheaddressesareoccupied,andunoccupiedaddressesmaynotbeimplementedonthechip.Readaccessestotheseaddresseswillingeneralreturnrandomdata,andwriteaccesseswillhaveanindeterminateeffect.Usersoftwareshouldnotwrite1stotheseunlistedlocations,sincetheymaybeusedinfutureproductstoinvokenewfeatures.Inthatcase,theresetorinactivevaluesofthenewbitswillalwaysbe0.

Timer2Registers:

ControlandstatusbitsarecontainedinregistersT2CONandT2MODforTimer2.Theregisterpair（RCAP2H,RCAP2L）aretheCapture/ReloadregistersforTimer2in16-bitcapturemodeor16-bitauto-reloadmode.

InterruptRegisters:

TheindividualinterruptenablebitsareintheIEregister.Twopriori-tiescanbesetforeachofthesixinterruptsourcesintheIPregister.

DataMemory:

TheAT89C52implements256bytesofon-chipRAM.Theupper128bytesoccupyaparalleladdressspacetotheSpecialFunctionRegisters.Thatmeanstheupper128Whenaninstructionaccessesaninternallocationaboveaddress7FH,theaddressmodeusedintheinstructionspecifieswhethertheCPUaccessestheupper128bytesofRAMortheSFRspace.InstructionsthatusedirectaddressingaccessSFRspace.Forexample,thefollowingdirectaddressinginstructionaccessestheSFRatlocation0A0H（whichisP2）.Instructionsthatuseindirectaddressingaccesstheupper128bytesofRAM.Forexample,thefollowingindirectaddressinginstruction,whereR0contains0A0H,accessesthedatabyteataddress0A0H,ratherthanP2（whoseaddressis0A0H）.Notethatstackoperationsareexamplesofindirectaddressing,sotheupper128bytesofdataRAMareavailableasstackspace.

Timer0and1:

Timer0andTimer1intheAT89C52operatethesamewayasTimer0andTimer1intheAT89C51.

Timer2:

Timer2isa16-bitTimer/Counterthatcanoperateaseitheratimeroraneventcounter.ThetypeofoperationisselectedbybitC/T2intheSFRT2CON.Timer2hasthreeoperatingmodes:

capture,auto-reload（upordowncounting）,andbaudrategenerator.ThemodesareselectedbybitsinT2CON.Timer2consistsoftwo8-bitregisters,TH2andTL2.IntheTimerfunction,theTL2registerisincrementedeverymachinecycle.Sinceamachinecycleconsistsof12oscillatorperiods,thecountrateis1/12oftheoscillatorfrequency.IntheCounterfunction,theregisterisincrementedinresponsetoa1-to-0transitionatitscorrespondingexternalinputpin,T2.Inthisfunction,theexternalinputissampledduringS5P2ofeverymachinecycle.Whenthesamplesshowahighinonecycleandalowinthenextcycle,thecountisincremented.ThenewcountvalueappearsintheregisterduringS3P1ofthecyclefollowingtheoneinwhichthetransitionwasdetected.Sincetwomachinecycles（24oscillatorperiods）arerequiredtorecognizea1-to-0transition,themaxi-mumcountrateis1/24oftheoscillatorfrequency.Toensurethatagivenlevelissampledatleastoncebeforeitchanges,thelevelshouldbeheldforatleastonefullmachinecycle.

CaptureMode:

Inthecapturemode,twooptionsareselectedbybitEXEN2inT2CON.IfEXEN2=0,Timer2isa16-bittimerorcounterwhichuponoverflowsetsbitTF2inT2CON.Thisbitcanthenbeusedtogenerateaninterrupt.IfEXEN2=1,Timer2performsthesameoperation,buta1-to-0transitionatexternalinputT2EXalsocausesthecurrentvalueinTH2andTL2tobecapturedintoRCAP2HandRCAP2L,respectively.Inaddition,thetransitionatT2EXcausesbitEXF2inT2CONtobeset.TheEXF2bit,likeTF2,cangenerateaninterrupt.

Auto-Reload（UporDownCounter）:

Timer2canbeprogrammedtocountupordownwhenconfiguredinits16-bitauto-reloadmode.ThisfeatureisinvokedbytheDCEN（DownCounterEnable）bitlocatedintheSFRT2MOD（seeTable4）.Uponreset,theDCENbitissetto0sothattimer2willdefaulttocountup.WhenDCENisset,Timer2cancountupordown,dependingonthevalueoftheT2EXpin.

Timer2automaticallycountupwhenDCEN=0.Inthismode,twooptionsareselectedbybitEXEN2inT2CON.IfEXEN2=0,Timer2countsupto0FFFFHandthensetstheTF2bituponoverflow.Theoverflowalsocausesthetimerregisterstobereloadedwiththe16-bitvalueinRCAP2HandRCAP2L.ThevaluesinTimerinCaptureModeRCAP2HandRCAP2Larepresetbysoftware.IfEXEN2=1,a16-bitreloadcanbetriggeredeitherbyanoverfloworbya1-to-0transitionatexternalinputT2EX.Thistransi-tionalsosetstheEXF2bit.BoththeTF2andEXF2bitscangenerateaninterruptifenabled.

SettingtheDCENbitenablesTimer2tocountupordown,asshowninFigure3.Inthismode,theT2EXpincontrolsthedirectionofthecount.Alogic1atT2EXmakesTimer2