文献翻译——微型计算机控制系统（单片机控制系统）

1外文文献资料MicrocomputerSystemsElectronicsystemsareusedforhandinginformationinthemostgeneralsense;thisinformationmaybetelephoneconversation,instrumentreadoracompanysaccounts,butineachcasethesamemaintypeofoperationareinvolved:theprocessing,storageandtransmissionofinformation.Inconventionalelectronicdesigntheseoperationsarecombinedatthefunctionlevel;forexampleacounter,whetherelectronicormechanical,storesthecurrentandincrementsitbyoneasrequired.Asystemsuchasanelectronicclockwhichemployscountershasitsstorageandprocessingcapabilitiesspreadthroughoutthesystembecauseeachcounterisabletostoreandprocessnumbers.Presentdaymicroprocessorbasedsystemsdepartfromthisconventionalapproachbyseparatingthethreefunctionsofprocessing,storage,andtransmissionintodifferentsectionofthesystem.ThispartitioningintothreemainfunctionswasdevisedbyVonNeumannduringthe1940s,andwasnotconceivedespeciallyformicrocomputers.Almosteverycomputerevermadehasbeendesignedwiththisstructure,anddespitetheenormousrangeintheirphysicalforms,theyhaveallbeenofessentiallythesamebasicdesign.Inamicroprocessorbasedsystemtheprocessingwillbeperformedinthemicroprocessoritself.Thestoragewillbebymeansofmemorycircuitsandthecommunicationofinformationintoandoutofthesystemwillbebymeansofspecialinput/output(I/O)circuits.Itwouldbeimpossibletoidentifyaparticularpieceofhardwarewhichperformedthecountinginamicroprocessorbasedclockbecausethe2timewouldbestoredinthememoryandincrementedatregularintervalsbutthemicroprocessor.However,thesoftwarewhichdefinedthesystemsbehaviorwouldcontainsectionsthatperformedascounters.Theapparentlyratherabstractapproachtothearchitectureofthemicroprocessoranditsassociatedcircuitsallowsittobeveryflexibleinuse,sincethesystemisdefinedalmostentirelysoftware.Thedesignprocessislargelyoneofsoftwareengineering,andthesimilarproblemsofconstructionandmaintenancewhichoccurinconventionalengineeringareencounteredwhenproducingsoftware.Thefigure1-1illustrateshowthesethreesectionswithinamicrocomputerareconnectedintermsofthecommunicationofinformationwithinthemachine.Thesystemiscontrolledbythemicroprocessorwhichsupervisesthetransferofinformationbetweenitselfandthememoryandinput/outputsections.Theexternalconnectionsrelatetotherest(thatis,thenon-computerpart)oftheengineeringsystem.Fig.1-1ThreeSectionsofaTypicalMicrocomputerAlthoughonlyonestoragesectionhasbeenshowninthediagram,inpracticetwodistincttypesofmemoryRAMandROMareused.Ineachcase,thewordmemoryisratherinappropriatesinceacomputersmemoryismorelikeafilingcabinetinconcept;informationisstoredinasetofnumberedboxesanditisreferencedbytheserialnumberoftheboxinquestion.MicrocomputersuseRAM(RandomAccessMemory)intowhichdatacanbewrittenandfromwhichdatacanbereadagainwhenneeded.Thisdatacanbereadbackfromthememoryinanysequencedesired,3andnotnecessarilythesameorderinwhichitwaswritten,hencetheexpressionrandomaccessmemory.AnothertypeofROM(ReadOnlyMemory)isusedtoholdfixedpatternsofinformationwhichcannotbeaffectedbythemicroprocessor;thesepatternsarenotlostwhenpowerisremovedandarenormallyusedtoholdtheprogramwhichdefinesthebehaviorofamicroprocessorbasedsystem.ROMscanbereadlikeRams,butunlikeRamstheycannotbeusedtostorevariableinformation.SomeROMshavetheirdatapatternsputinduringmanufacture,whileothersareprogrammablebytheuserbymeansofspecialequipmentandarecalledprogrammableROMs.ThewidelyusedprogrammableROMsareerasablebymeansofspecialultravioletlampsandarereferredtoasEPROMs,shortforErasableProgrammableReadOnlyMemories.Othernewtypesofdevicecanbeerasedelectricallywithouttheneedforultravioletlight,whicharecalledElectricallyErasableProgrammableReadOnlyMemories,EPROMs.Themicroprocessorprocessesdataunderthecontroloftheprogram,controllingtheflowofinformationtoandfrommemoryandinput/outputdevices.Someinput/outputdevicesaregeneral-purposetypeswhileothersaredesignedforcontrollingspecialhardwaresuchasdiscdrivesorcontrollinginformationtransmissiontoothercomputers.MosttypesofI/Odevicesareprogrammabletosomeextent,allowingdifferentmodesofoperation,whilesomeactuallycontainspecial-purposemicroprocessorstopermitquitecomplexoperationstobecarriedoutwithoutdirectlyinvolvingthemainmicroprocessor.Themicroprocessorprocessesdataunderthecontroloftheprogram,controllingtheflowofinformationtoandfrommemoryandinput/outputdevices.Someinput/outputdevicesaregeneral-purposetypeswhileothersaredesignedforcontrollingspecialhardwaresuchasdiscdrivesorcontrollinginformationtransmissiontoothercomputers.MosttypesofI/Odevicesareprogrammabletosomeextent,allowingdifferentmodesofoperation,whilesomeactuallycontain4special-purposemicroprocessorstopermitquitecomplexoperationstobecarriedoutwithoutdirectlyinvolvingthemainmicroprocessor.Themicroprocessor,memoryandinput/outputcircuitmayallbecontainedonthesameintegratedcircuitprovidedthattheapplicationdoesnotrequiretoomuchprogramordatastorage.Thisisusuallythecaseinlow-costapplicationsuchasthecontrollersusedinmicrowaveovensandautomaticwashingmachines.Theuseofsinglepackageallowsconsiderablecostsavingstoemadewhenarticlesaremanufacturedinlargequantities.Astechnologydevelops,moreandmorepowerfulprocessorsandlargerandlargeramountsofmemoryarebeingincorporatedintosinglechipmicrocomputerswithresultingsavinginassemblycostsinthefinalproducts.Fortheforeseeablefuture,however,itwillcontinuetobenecessarytointerconnectanumberofintegratedcircuitstomakeamicrocomputerwheneverlargeramountsofstorageorinput/outputarerequired.Anothermajorengineeringapplicationofmicrocomputersisinprocesscontrol.Herethepresenceofthemicrocomputerisusuallymoreapparenttotheuserbecauseprovisionisnormallymadeforprogrammingthemicrocomputerfortheparticularapplication.Inprocesscontrolapplicationsthebenefitslffittingtheentiresystemontosinglechipareusuallyoutweighedbythehighdesigncostinvolved,becausethissortlfequipmentisproducedinsmallerquantities.Moreover,processcontrollersareusuallymorecomplicatedsothatitismoredifficulttomakethemassingleintegratedcircuits.Twoapproachesarepossible;thecontrollercanbeimplementedasageneral-purposemicrocomputerratherlikeamorerobustversionlfahobbycomputer,orasapackagedsystem,signedforreplacingcontrollersbasedonoldertechnologiessuchaselectromagneticrelays.Intheformercasethesystemwouldprobablybeprogrammedinconventionalprogramming5languagessuchastheonesto9beintroducedlater,whileintheothercaseaspecial-purposelanguagemightbeused,forexampleonewhichallowedthefunctionofthecontrollertobedescribedintermsofrelayinterconnections,IneithercaseprogramscanbestoredinRAM,whichallowsthemtobealteredtosuitchangesinapplication,butthismakestheoverallsystemvulnerabletolosslfpowerunlessbatteriesareusedtoensurecontinuityofsupply.AlternativelyprogramscanbestoredinROM,inwhichcasetheyvirtuallybecomepartoftheelectronichardwareandareoftenreferredtoasfirmware.Moresophisticatedprocesscontrollersrequireminicomputersfortheirimplementation,althoughtheuselflargescaleintegratedcircuitsthedistinctionbetweenminiandmicrocomputers,Productsandprocesscontrollersofvariouskindsrepresentthemajorityofpresent-daymicrocomputerapplications,theexactfiguresdependingononesinterpretationofthewordproduct.Virtuallyallengineeringandscientificusesofmicrocomputerscanbeassignedtooneorotherofthesecategories.ButinthesystemwemoststudyPressureandPressureTransmitters.Pressureariseswhenaforceisappliedoveranarea.ProvidedtheforceisoneNewtonanduniformlyovertheareaofonesquaremeters,thepressurehasbeendesignatedonePascal.Pressureisauniversalprocessingcondition.Itisalsoaconditionoflifeontheplanet:weliveatthebottomofanatmosphericoceanthatextendsupwardformanymiles.Thismassofairhasweight,andthisweightpressingdownwardcausesatmosphericpressure.Water,afundamentalnecessityoflife,issuppliedtomostofusunderpressure.Inthetypicalprocessplant,pressureinfluencesboilingpointtemperatures,condensingpointtemperatures,processefficiency,costs,andotherimportantfactors.Themeasurementandcontrolofpressureorlackofit-vacuum-inthetypicalprocessplantiscritical.6Theworkinginstrumentsintheplantusuallyincludesimplepressuregauges,precisionrecordersandindicators,andpneumaticandelectronicpressuretransmitters.Apressuretransmittermakesapressuremeasurementandgenerateseitherapneumaticorelectricalsignaloutputthatisproportionaltothepressurebeingsensed.Intheprocessplant,itisimpracticaltolocatethecontrolinstrumentsoutintheplaceneartheprocess.Itisalsotruethatmostmeasurementsarenoteasilytransmittedfromsomeremotelocation.Pressuremeasurementisanexception,butifahighpressureofsomedangerouschemicalistobeindicatedorrecordedseveralhundredfeetfromthepointofmeasurement,ahazardmaybefromthepressureorfromthechemicalcarried.Toeliminatethisproblem,asignaltransmissionsystemwasdeveloped.Thissystemisusuallyeitherpneumaticorelectrical.Andcontrolinstrumentsinonelocation.Thismakesitpracticalforaminimumnumberofoperatorstoruntheplantefficiently.Whenapneumatictransmissionsystemisemployed,themeasurementsignalisconvertedintopneumaticsignalbythetransmitterscaledfrom0to100percentofthemeasurementvalue.Thistransmitterismountedclosetothepointofmeasurementintheprocess.Thetransmitteroutput-airpressureforapneumatictransmitter-ispipedtotherecordingorcontrolinstrument.Thestandardoutputrangeforapneumatictransmitteris20to100kPa,whichisalmostuniversallyused.Whenanelectronicpressuretransmitterisused,thepressureisconvertedtoelectricalsignalthatmaybecurrentorvoltage.Itsstandardrangeisfrom4to20mADCforcurrentsignalorfrom1to5VDCforvoltagesignal.Nowadays,anothertypeofelectricalsignal,whichisbecomingcommon,isthedigitalordiscretesignal.Theuseofinstrumentsandcontrolsystemsbasedoncomputerorforcingincreaseduseofthistypeofsignal.7Sometimesitisimportantforanalysistoobtaintheparametersthatdescribethesensor/transmitterbehavior.Thegainisfairlysimpletoobtainoncethespanisknown.Consideranelectronicpressuretransmitterwitharangeof0600kPa.ThegainisDefinedasthechangeinoutputdividedbythechangeininput.Inthiscase,theoutputiselectricalsignal(420mADC)andtheinputisprocesspressure(0600kPa).Thusthegain.BesidewemustmeasureTemperatureTemperaturemeasurementisimportantinindustrialcontrol,asdirectindicationsofsystemorproductstateandasindirectindicationsofsuchfactorsasreactionrates,energyflow,turbineefficiency,andlubricantquality.Presenttemperaturescaleshavebeeninuseforabout200years,theearliestinstrumentswerebasedonthethermalexpansionofgasesandliquids.Suchfilledsystemsarestillemployed,althoughmanyothertypesofinstrumentsareavailable.Representativetemperaturesensorsinclude:filledthermalsystems,liquid-in-glassthermometers,thermocouples,resistancetemperaturedetectors,thermostats,bimetallicdevices,opticalandradiationpyrometersandtemperature-sensitivepaints.Advantagesofelectricalsystemsincludehighaccuracyandsensitivity,practicalityofswitchingorscanningseveralmeasurementspoints,largerdistancespossiblebetweenmeasuringelementsandcontrollers,replacementofcomponents(ratherthancompletesystem),fastresponse,andabilitytomeasurehighertemperature.Amongtheelectricaltemperaturesensors,thermocouplesandresistancetemperaturedetectorsaremostwidelyused.DescriptionTheAT89C51isalow-power,high-performanceCMOS8-bitmicrocomputerwith4KbytesofFlashprogrammableanderasablereadonlymemory(PEROM).ThedeviceismanufacturedusingAtmelshigh-densitynonvolatilememorytechnologyandiscompatiblewiththeindustry-kPamAkPakmAKr027.616428standardMCS-51instructionsetandpinout.Theon-chipFlashallowstheprogrammemorytobereprogrammedin-systemorbyaconventionalnonvolatilememoryprogrammer.Bycombiningaversatile8-bitCPUwithFlashonamonolithicchip,theAtmelAT89C51isapowerfulmicrocomputerwhichprovidesahighly-flexibleandcost-effectivesolutiontomanyembeddedcontrolapplications.Functioncharacteristic：TheAT89C51providesthefollowingstandardfeatures:4KbytesofFlash,128bytesofRAM,32I/Olines,two16-bittimer/counters,fivevectortwo-levelinterruptarchitecture,afullduplexserialport,andon-chiposcillatorandclockcircuitry.Inaddition,theAT89C51isdesignedwithstaticlogicforoperationdowntozerofrequencyandsupportstwosoftwareselectablepowersavingmodes.TheIdleModestopstheCPUwhileallowingtheRAM,timer/counters,serialportandinterruptsystemtocontinuefunctioning.ThePower-downModesavestheRAMcontentsbutfreezestheoscillatordisablingallotherchipfunctionsuntilthenexthardwarereset.PinDescription：VCC：Supplyvoltage.GND：Ground.Port0：Port0isan8-bitopen-drainbi-directionalI/Oport.Asanoutputport,eachpincansinkeightTTLinputs.When1sarewrittentoport0pins,thepinscanbeusedashighimpedanceinputs.Port0mayalsobeconfiguredtobethemultiplexedloworderaddress/databusduringaccessestoexternalprogramanddatamemory.InthismodeP0hasinternalpullups.Port0alsoreceivesthecodebytesduringFlashprogramming,andoutputsthecodebytesduringprogramverification.Externalpullupsarerequiredduringprogramverification.Port1Port1isan8-bitbi-directionalI/Oportwithinternalpullups.The9Port1outputbufferscansink/sourcefourTTLinputs.When1sarewrittentoPort1pinstheyarepulledhighbytheinternalpullupsandcanbeusedasinputs.Asinputs,Port1pinsthatareexternallybeingpulledlowwillsourcecurrent(IIL)becauseoftheinternalpullups.Port1alsoreceivesthelow-orderaddressbytesduringFlashprogrammingandverification.Port2Port2isan8-bitbi-directionalI/Oportwithinternalpullups.ThePort2outputbufferscansink/sourcefourTTLinputs.When1sarewrittentoPort2pinstheyarepulledhighbytheinternalpullupsandcanbeusedasinputs.Asinputs,Port2pinsthatareexternallybeingpulledlowwillsourcecurrent,becauseoftheinternalpullups.Port2emitsthehigh-orderaddressbyteduringfetchesfromexternalprogrammemoryandduringaccessestoexternaldatamemorythatuse16-bitaddresses.Inthisapplication,itusesstronginternalpullupswhenemitting1s.Duringaccessestoexternaldatamemorythatuse8-bitaddresses,Port2emitsthecontentsoftheP2SpecialFunctionRegister.Port2alsoreceivesthehigh-orderaddressbitsandsomecontrolsignalsduringFlashprogrammingandverification.Port3Port3isan8-bitbi-directionalI/Oportwithinternalpullups.ThePort3outputbufferscansink/sourcefourTTLinputs.When1sarewrittentoPort3pinstheyarepulledhighbytheinternalpullupsandcanbeusedasinputs.Asinputs,Port3pinsthatareexternallybeingpulledlowwillsourcecurrent(IIL)becauseofthepullups.Port3alsoservesthefunctionsofvariousspecialfeaturesoftheAT89C51aslistedbelow:Port3alsoreceivessomecontrolsignalsforFlashprogrammingandverification.RST10Resetinput.Ahighonthispinfortwomachinecycleswhiletheoscillatorisrunningresetsthedevice.ALE/PROGAddressLatchEnableoutputpulseforlatchingthelowbyteoftheaddressduringaccessestoexternalmemory.Thispinisalsotheprogrampulseinput(PROG)duringFlashprogramming.InnormaloperationALEisemittedataconstantrateof1/6theoscillatorfrequency,andmaybeusedforexternaltimingorclockingpurposes.Note,however,thatoneALEpulseisskippedduringeachaccesstoexternalDataMemory.Ifdesired,ALEoperationcanbedisabledbysettingbit0ofSFRlocation8EH.Withthebitset,ALEisactiveonlyduringaMOVXorMOVCinstruction.Otherwise,thepinisweaklypulledhigh.SettingtheALE-disablebithasnoeffectifthemicrocontrollerisinexternalexecutionmode.PSENProgramStoreEnableisthereadstrobetoexternalprogrammemory.WhentheAT89C51isexecutingcodefromexternalprogrammemory,PSENisactivatedtwiceeachmachinecycle,exceptthattwoPSENactivationsareskippedduringeachaccesstoexternaldatamemory.EA/VPPExternalAccessEnable.EAmustbestrappedtoGNDinordertoenablethedevicetofetchcodefromexternalprogrammemorylocationsstartingat0000HuptoFFFFH.Note,however,thatiflockbit1isprogrammed,EAwillbeinternallylatchedonreset.EAshouldbestrappedtoVCCforinternalprogramexecutions.Thispinalsoreceivesthe12-voltprogrammingenablevoltage(VPP)duringFlashprogramming,forpartsthatrequire12-voltVPP.XTAL1Inputtotheinvertingoscillatoramplifierandinputtotheinternalclockoperatingcircuit.XTAL211Outputfromtheinvertingoscillatoramplifier.OscillatorCharacteristicsXTAL1andXTAL2aretheinputandoutput,respectively,ofaninvertingamplifierwhichcanbeconfiguredforuseasanon-chiposcillator,asshowninFigure1.Eitheraquartzcrystalorceramicresonatormaybeused.Todrivethedevicefromanexternalclocksource,XTAL2shouldbeleftunconnectedwhileXTAL1isdrivenasshowninFigure2.Therearenorequirementsonthedutycycleoftheexternalclocksignal,sincetheinputtotheinternalclockingcircuitryisthroughadivide-by-twoflip-flop,butminimumandmaximumvoltagehighandlowtimespecificationsmustbeobserved中文翻译资料微型计算机控制系统（单片机控制系统）广义地说，微型计算机控制系统（单片机控制系统）是用于处理信息的，这种被用于处理的信息可以是电话交谈，也可以是仪器的读数或者是一个企业的账户，但是各种情况下都涉及到相同的主要操作：信息的处理、信息的存储和信息的传递。在常规的电子设计中，这些操作都是以功能平台方式组合起来的，例如计数器，无论是电子计数器还是机械计数器，都要存储当前的数值，并且按要求将该数值增加1。一个系统例如采用计数器的电子钟之类的任一系统要使其存储和处理能力遍布整个系统，因为每个计数器都能存储和处理一些数字。现如今，以微处理器为基础的系统从常规的处理方法中分离了出来，它将信息的处理，信息的存储和信息的传输三个功能分离形成不同的系统单元。这种主要将系统分成三个主要单元的分离方法是冯-诺依曼在20世纪40年代所设想出来的，并且是针对微计算机的设想。从此以后基本上所有制成的计算机都12是用这种结构设计的，尽管他们包含着宽广的物理形式与物理结构，但从根本上来说他们均是具有相同基本设计的计算机。在以微处理器为基础的系统中，处理是由以微处理器为基础的系统自身完成的。存储是利用存储器电路，而从系统中输入和输出的信息传输则是利用特定的输入/输出（I/O）电路。要在一个以微处理器为基础的时钟中找出执行具有计数功能的一个特殊的硬件组成部分是不可能的，因为时间存储在存储器中，而在固定的时间间隔下由微处理器控制增值。但是，规定系统运转过程的软件却规定了包含实现计数器计数功能的单元部分。由于系统几乎完全由软件所定义，所以对微处理器结构和其辅助电路这种看起来非常抽象的处理方法使其在应用时非常灵活。这种设计过程主要是软件工程，而且在生产软件时，就会遇到产生于常规工程中相似的构造和维护问题。图图1-1微型计算机的三个组成部分图1-1显示出了微型计算机中这三个单元在一个微处理器控制系统中是如何按照机器中的信息通信方式而联接起来的。该系统由微处理器控制，微处理器能够对其自身的存储器和输入/输出单元的信息传输进行管理。外部的连接部分与工程系统中的其余部分（即非计算机部分）有关。尽管图中显示的只有一个存储单元，但是在实际中却有RAM和ROM两种不同的存储器被使用。在每一种情况下，由于概念上的计算机存储器更像一个公文柜，上述的“存储器”一词是非常不恰当的；信息被存放在一系列经数字标记过的的“箱子”中，而且可以按照问题由“箱子”的序列号进行相关信息的参考定位。微计算机控制系统经常使用RAM（随机存取存储器），在RAM中，数据可以被写入，并且在需要的时候，可以被再次读出。这种数据能以任意一种所希望的次序从存储器中读出，而不必按照写入时的相同次序读出，所以有“随机”存取存储器。另一类型ROM（只读存储器）是用来保持信息的，它们是不受微13处理器影响的固定的信息标本；这些信息在电源切断后不会丢失，并通常用来保存规定微处理器化系统运转过程的程序。ROM可像RAM一样被读取，但与RAM不一样的是不能用来存储可变的信息。有些ROM在制造时将其数据标本放入，而另外的则可通过特殊的设备由用户编程，所以称为可编程ROM。被广泛使用的可编程ROM可利用特殊紫外线灯擦除，并被成为EPROM，即可擦除可编程只读存储器的缩写。另有新类型的期器件不必用紫外线灯而用电察除，所以称为电可擦除可编程只读存储器EEPROM。微处理器在程序控制下处理数据，并控制流向和来自存储器和输入/输出装置的信息流。有些输入/输出装置是通用型的，而另外一些则是设计来控制如磁盘驱动器的特殊硬件，或控制传给其他计算机的信息传输。大多数类型的I/O装置在某种程度下可编程，允许不同形式的操作，而有些则包含特殊用途微处理器的I/O装置不用主微处理器的直接干预，就可实施非常复杂的操作。假如应用中不需要太多的程序和数据存储量，微处理器、存储器和输入/输出可全被包含在同一集成电路中。这通常是低成本应用情况，例如用于微波炉和自动洗衣机的控制器。当商品被大量地生产时，这种单一芯片的使用就可节省相当大的成本。当技术进一步发展，更强的处理器和更大数量的存储器被包含形成单片微型计算机，结果使最终产品的装配成本得以节省。但是在可预见的未来，当需要大量的存储器或输入/输出时，还是有必要继续将许多集成电路相互联结起来，形成微计算机。微计算机的另一主要工程应用是在过程控制中。这是，由于装置是按特定的应用情况由微机编程实现的，对用户来说微计算机的存在通常就更加明显。在过程控制应用中，由于这种设备以较少的数量生产，将整个系统安装在单个芯片上所获取的利益常比不上所涉及的设计成本。而且，过