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1、外文原文外文原文TheIntroductionofAT89C51DeionTheAT89C51isalowpowerhighperfmanceCMOS8bitmicrocomputerwith4KbytesofFlashprogrammableerasablereadonlymemy(PEROM).ThedeviceismanufacturedusingAtmel’shighdensitynonvolatilememytechnolog

2、yiscompatiblewiththeindustrystardMCS51instructionsetpinout.TheonchipFlashallowstheprogrammemytobereprogrammedinsystembyaconventionalnonvolatilememyprogrammer.Bycombiningaversatile8bitCPUwithFlashonamonolithicchiptheAtmel

3、AT89C51isapowerfulmicrocomputerwhichprovidesahighlyflexiblecosteffectivesolutiontomanyembeddedcontrolapplications.FunctionacteristicTheAT89C51providesthefollowingstardfeatures:4KbytesofFlash128bytesofRAM32IOlinestwo16bit

4、timercountersafivevecttwolevelinterruptarchitectureafullduplexserialptonchiposcillatclockcircuitry.InadditiontheAT89C51isdesignedwithstaticlogicfoperationdowntozerofrequencysupptstwosoftwareablepowersavingmodes.TheIdleMo

5、destopstheCPUwhileallowingtheRAMtimercountersserialptinterruptsystemtocontinuefunctioning.ThePowerdownModesavestheRAMcontentsbutfreezestheoscillatdisablingallotherchipfunctionsuntilthenexthardwarereset.PinDeionVCC：Supply

6、voltage.GND：Ground.Pt0：Pt0isan8bitopendrainbidirectionalIOpt.AsanoutputpteachpincansinkeightTTLinputs.When1sarewrittentopt0pinsthepinscanbeusedashighimpedanceinputs.Pt0mayalsobeconfiguredtobethemultiplexedlowderaddressda

7、tabusduringaccessestoexternalprogramdatamemy.InthismodeP0hasinternalpullups.Pt0alsoreceivesthecodebytesduringFlashprogrammingoutputsthecodebytesduringprogramverification.Externalpullupsarerequiredduringprogramverificatio

8、n.Pt3alsoreceivessomecontrolsignalsfFlashprogrammingverification.RSTResetinput.Ahighonthispinftwomachinecycleswhiletheoscillatisrunningresetsthedevice.ALEPROGAddressLatchEnableoutputpulseflatchingthelowbyteoftheaddressdu

9、ringaccessestoexternalmemy.Thispinisalsotheprogrampulseinput(PROG)duringFlashprogramming.InnmaloperationALEisemittedataconstantrateof16theoscillatfrequencymaybeusedfexternaltimingclockingpurposes.NotehoweverthatoneALEpul

10、seisskippedduringeachaccesstoexternalDataMemy.IfdesiredALEoperationcanbedisabledbysettingbit0ofSFRlocation8EH.WiththebitsetALEisactiveonlyduringaMOVXMOVCinstruction.Otherwisethepinisweaklypulledhigh.SettingtheALEdisableb

11、ithasnoeffectifthemicrocontrollerisinexternalexecutionmode.PSENProgramSteEnableisthereadstrobetoexternalprogrammemy.WhentheAT89C51isexecutingcodefromexternalprogrammemyPSENisactivatedtwiceeachmachinecycleexceptthattwoPSE

12、Nactivationsareskippedduringeachaccesstoexternaldatamemy.EAVPPExternalAccessEnable.EAmustbestrappedtoGNDindertoenablethedevicetofetchcodefromexternalprogrammemylocationsstartingat0000HuptoFFFFH.Notehoweverthatiflockbit1i

13、sprogrammedEAwillbeinternallylatchedonreset.EAshouldbestrappedtoVCCfinternalprogramexecutions.Thispinalsoreceivesthe12voltprogrammingenablevoltage(VPP)duringFlashprogrammingfpartsthatrequire12voltVPP.XTAL1Inputtotheinver

14、tingoscillatamplifierinputtotheinternalclockoperatingcircuit.XTAL2Outputfromtheinvertingoscillatamplifier.OscillatacteristicsXTAL1XTAL2aretheinputoutputrespectivelyofaninvertingamplifierwhichcanbeconfiguredfuseasanonchip

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