通信工程专业英语论文.docx

通信工程专业英语论文.docx

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通信工程专业英语论文

TheGeneralSituationofAT89C51

TheAT89C51isalow-power,high-performanceCMOS8-bitmicrocomputerwith4KbytesofFlashProgrammableandErasableReadOnlyMemory（PEROM）and128bytesRAM.ThedeviceismanufacturedusingAtmel’shighdensitynonvolatilememorytechnologyandiscompatiblewiththeindustrystandardMCS-51™instructionsetandpinout.Thechipcombinesaversatile8-bitCPUwithFlashonamonolithicchip;theAtmelAT89C51isapowerfulmicrocomputerwhichprovidesahighlyflexibleandcosteffectivesolutiontomanyembeddedcontrolapplications.

Features:

•CompatiblewithMCS-51™Products

•4KBytesofIn-SystemReprogrammableFlashMemory

•Endurance:

1,000Write/EraseCycles

•FullyStaticOperation:

0Hzto24MHz

•Three-LevelProgramMemoryLock

•128x8-BitInternalRAM

•32ProgrammableI/OLines

•Two16-BitTimer/Counters

•SixInterruptSources

•ProgrammableSerialChannel

•LowPowerIdleandPowerDownModes

TheAT89C51providesthefollowingstandardfeatures:

4KbytesofFlash,128bytesofRAM,32I/Olines,two16-bittimer/counters,afivevectortwo-levelinterruptarchitecture,afullduplexserialport,on-chiposcillatorandclockcircuitry.Inaddition,theAT89C51isdesignedwithstaticlogicforoperationdowntozerofrequencyandsupportstwosoftwareselectablepowersavingmodes.TheIdleModestopstheCPUwhileallowingtheRAM,timer/counters,serialportandinterruptsystemtocontinuefunctioning.ThePowerDownModesavestheRAMcontentsbutfreezestheoscillatordisablingallotherchipfunctionsuntilthenexthardwarereset.

BlockDiagram

PinDescription:

VCCSupplyvoltage.

GNDGround.

Port0：

Port0isan8-bitopendrainbidirectionalI/Oport.AsanoutputporteachpincansinkeightTTLinputs.When1sarewrittentoport0pins,thepinscanbeusedashighimpedanceinputs.（Sink/flow）

Port0mayalsobeconfiguredtobethemultiplexedloworderaddress/databusduringaccessestoexternalprogramanddatamemory.InthismodeP0hasinternalpull-ups.

Port0alsoreceivesthecodebytesduringFlashprogramming,andoutputsthecodebytesduringprogramverification.Externalpull-upsarerequiredduringprogramverification.

Port1：

Port1isan8-bitbidirectionalI/Oportwithinternalpull-ups.ThePort1outputbufferscansink/sourcefourTTLinputs.When1sarewrittentoPort1pinstheyarepulledhighbytheinternalpull-upsandcanbeusedasinputs.Asinputs,Port1pinsthatareexternallybeingpulledlowwillsourcecurrent（IIL）becauseoftheinternalpull-ups.

Port1alsoreceivesthelow-orderaddressbytesduringFlashprogrammingandverification.

Port2：

Port2isan8-bitbidirectionalI/Oportwithinternalpull-ups.ThePort2outputbufferscansink/sourcefourTTLinputs.When1sarewrittentoPort2pinstheyarepulledhighbytheinternalpull-upsandcanbeusedasinputs.Asinputs,Port2pinsthatareexternallybeingpulledlowwillsourcecurrent（IIL）becauseoftheinternalpull-ups.

Port2emitsthehigh-orderaddressbyteduringfetchesfromexternalprogrammemoryandduringaccessestoexternaldatamemorythatuses16-bitaddresses（MOVX@DPTR）.Inthisapplicationitusesstronginternalpull-upswhenemitting1s.Duringaccessestoexternaldatamemoriesthatuse8-bitaddresses（MOVX@RI）,Port2emitsthecontentsoftheP2SpecialFunctionRegister.

Port2alsoreceivesthehigh-orderaddressbitsandsomecontrolsignalsduringFlashprogrammingandverification.

Port3：

Port3isan8-bitbidirectionalI/Oportwithinternalpull-ups.ThePort3outputbufferscansink/sourcefourTTLinputs.When1sarewrittentoPort3pinstheyarepulledhighbytheinternalpull-upsandcanbeusedasinputs.Asinputs,Port3pinsthatareexternallybeingpulledlowwillsourcecurrent（IIL）becauseofthepull-ups.

Port3alsoservesthefunctionsofvariousspecialfeaturesoftheAT89C51aslistedbelow:

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）

Port3alsoreceivessomecontrolsignalsforFlashprogrammingandverification.

RST：

Resetinput.Ahighonthispinfortwomachinecycleswhiletheoscillatorisrunningresetsthedevice.

ALE/PROG：

AddressLatchEnableoutputpulseforlatchingthelowbyteoftheaddressduringaccessestoexternalmemory.Thispinisalsotheprogrampulseinput（PROG）duringFlashprogramming.

InnormaloperationALEisemittedataconstantrateof1/6theoscillatorfrequency,andmaybeusedforexternaltimingorclockingpurposes.Note,however,thatoneALEpulseisskippedduringeachaccesstoexternalDataMemory.

Ifdesired,ALEoperationcanbedisabledbysettingbit0ofSFRlocation8EH.Withthebitset,ALEisactiveonlyduringaMOVXorMOVCinstruction.Otherwise,thepinisweaklypulledhigh.SettingtheALE-disablebithasnoeffectifthemicrocontrollerisinexternalexecutionmode.

PSEN：

ProgramStoreEnableisthereadstrobetoexternalprogrammemory.

WhentheAT89C51isexecutingcodefromexternalprogrammemory,PSENisactivatedtwiceeachmachinecycle,exceptthattwoPSENactivationsareskippedduringeachaccesstoexternaldatamemory.

EA/VPP：

ExternalAccessEnable.EAmustbestrappedtoGNDinordertoenablethedevicetofetchcodefromexternalprogrammemorylocationsstartingat0000HuptoFFFFH.Note,however,thatiflockbit1（LB1）isprogrammed,EAwillbeinternallylatched（fastenwithalatch）onreset.

EAshouldbestrappedtoVCCforinternalprogramexecutions.

Thispinalsoreceivesthe12-voltprogrammingenablevoltage（VPP）duringFlashprogramming,forpartsthatrequire12-voltVPP.

XTAL1：

Inputtotheinvertingoscillatoramplifierandinputtotheinternalclockoperatingcircuit.

XTAL2：

Outputfromtheinvertingoscillatoramplifier.

OscillatorCharacteristics：

XTAL1andXTAL2aretheinputandoutput,respectively,ofaninvertingamplifierwhichcanbeconfiguredforuseasanon-chiposcillator,asshowninFigure1.Eitheraquartzcrystalorceramicresonatormaybeused.Todrivethedevicefromanexternalclocksource,XTAL2shouldbeleftunconnectedwhileXTAL1isdrivenasshowninFigure2.Therearenorequirementsonthedutycycleoftheexternalclocksignal,sincetheinputtotheinternalclockingcircuitryisthroughadivide-by-twoflip-flop,butminimumandmaximumvoltagehighandlowtimesspecificationsmustbeobserved.

IdleMode：

Inidlemode,theCPUputsitselftosleepwhilealltheonchipperipheralsremainactive.Themodeisinvokedbysoftware.Thecontentoftheon-chipRAMandallthespecialfunctionsregistersremainunchangedduringthismode.Theidlemodecanbeterminatedbyanyenabledinterruptorbyahardwarereset.

Itshouldbenotedthatwhenidleisterminatedbyahardwarereset,thedevicenormallyresumesprogramexecution,fromwhereitleftoff,uptotwomachinecyclesbeforetheinternalresetalgorithmtakescontrol.On-chiphardwareinhibitsaccesstointernalRAMinthisevent,butaccesstotheportpinsisnotinhibited.ToeliminatethepossibilityofanunexpectedwritetoaportpinwhenIdleisterminatedbyreset,theinstructionfollowingtheonethatinvokesIdleshouldnotbeonethatwritestoaportpinortoexternalmemory.

StatusofExternalPinsDuringIdleandPowerDownModes

mode

Programmemory

ALE

^psen

Port0

Port1

Port2

Port3

idle

internal

1

1

data

data

data

Data

Idle

External

1

1

float

Data

data

Data

Powerdown

Internal

0

0

Data

Data

Data

Data

Powerdown

External

0

0

float

data

Data

data

PowerDownMode

Inthepowerdownmodetheoscillatorisstopped,andtheinstructionthatinvokespowerdownisthelastinstructionexecuted.Theon-chipRAMandSpecialFunctionRegistersretaintheirvaluesuntilthepowerdownmodeisterminated.Theonlyexitfrompowerdownisahardwarereset.ResetredefinestheSFRsbutdoesnotchangetheon-chipRAM.TheresetshouldnotbeactivatedbeforeVCCisrestoredtoitsnormaloperatinglevelandmustbeheldactivelongenoughtoallowtheoscillatortorestartandstabilize.

ProgramMemoryLockBits

Onthechiparethreelockbitswhichcanbeleftunprogrammed（U）orcanbeprogrammed（P）toobtaintheadditionalfeatureslistedinthetablebelow:

LockBitProtectionModes

Programlockbits

Protectiontype

Lb1

Lb2

Lb3

1

U

U

U

Noprogramlockfeatures

2

P

U

U

Movcinstructionsexecutedfromexternalprogrammemoryaredisablefromfetchingcodebytesfrominternalmemory,^eaissampledandlatchedonreset,andfurtherprogrammingoftheflashdisabled

3

P

P

U

Sameasmode2,alsoverifyisdisable.

4

P

P

P

Sameasmode3,alsoexternalexecutionisdisabled.

Whenlockbit1isprogrammed,thelogiclevelattheEApinissampledandlatchedduringreset.Ifthedeviceispoweredupwithoutareset,thelatchinitializestoarandomvalue,andholdsthatvalueuntilresetisactivated.ItisnecessarythatthelatchedvalueofEAbeinagreementwiththecurrentlogiclevelatthatpininorderforthedevicetofunctionproperly.

ProgrammingtheFlash：

TheAT89C51isnormallyshippedwiththeon-chipFlashmemoryarrayintheerasedstate（thatis,contents=FFH）andreadytobeprogrammed.Theprogramminginterfaceacceptseitherahigh-voltage（12-volt）oralow-voltage（VCC）programenablesignal.ThelowvoltageprogrammingmodeprovidesaconvenientwaytoprogramtheAT89C51insidetheuser’ssys