外文翻译--工程中的微型计算机.doc
英文翻译-1英文翻译资料SystemsUsingMicroprocessorsElectronicsystemsareusedforhandlinginformationinthemostgeneralsense;thisinformationmaybetelephoneconversation,instrumentreadingoracompanysaccounts,butineachcasethesamemaintypesofoperationareinvolved:theprocessing,storageandtransmissionofinformation.Inconventionalelectronicdesigntheseoperationsarecombinedatthefunctionlevel:forexampleacounter,whetherelectronicormechanical,storesthecurrentcountandincrementsitbyoneasrequired.AsystemsuchasanelectronicclockwhichemployscountershasitsstorageandprocessingcapabilitiesspreadthroughoutthesystembecauseeachcounterisabletostoreandProcessnumbers.Presentdaymicroprocessorbasedsystemsdepartfromthisconventionalapproachbyseparatingthethreefunctionsofprocessing,storage,andtransmissionintodifferentsectionofthesystem.ThispartitioningintothreemainfunctionswasdevisedbyVonNeumannduringthe1940s,andwasnotconceivedespeciallyformicrocomputers.Almosteverycomputerevermadehasbeendesignedwiththisstructure,anddespitetheenormousrangeintheirPhysicalforms,theyhaveallbeenofessentiallythesamebasicdesign.InamicroprocerrorbasedsystemtheProcessingwillbeperformedinthemicroprocessorsoitself.Thestoragewillbebymeansofmemorycircuitsandthecommunicationofinformationintoandoutofthesystemwillbebymeansofspecialinput/output(I/O)circuits.Itwouldbeimpossibletoidentifyaparticularpieceofhardwarewhichperformedthecountinginamicroprocessorbasedclockbecausethetimewouldbestoredinthememoryandincrementedatregularintervalsbythemicroprocessor.However,thesoftwarewhichdefinedthesystemsbehaviorwouldcontainsectionsthatperformedascountersTheapparentlyratherabstractapproachtothearchitectureofthemicroprocessoranditsassociatedcircuitsallowsittobeveryflexibleinuse,sincethesystemisdefinedalmostentirelyinsoftwareThedesignprocessislargelyoneofsoftwareengineering,andthesimilarproblemsofconstructionandmaintenancewhichoccurinconventionalengineeringareencounteredwhenproducingsoftware.英文翻译-2Figure15.1illustrateshowthesethreesessionswithinamicrocomputerareconnectedintermsofthecommunicationofinformationwithinthemachineThesystemiscontrolledbythemicroprocessorwhichsupervisesthetransferofinformationbetweenitselfandthememoryandinput/outputsections.Theexternalconnectionsrelatetotherest(thatis,thenon-computerpart)oftheengineeringsystem.Fig.15.1ThreeSectionsofaTypicalMicrocomputerAlthoughonlyonestoragesectionhasbeenshowninthediagram,inpracticetwodistincttypesofmemoryRAMandROMareusedIneachcase,thewordmemoryisratherinappropriatesinceacomputermemoryismorelikeafilingcabinetinconcept;Informationisstoredinasetofnumberedboxesbanditosreferencedbytheserialnumberoftheboxinquestion.MicrocomputersuseRAM(RandomAccessMemoryintowhichdatacanbewrittenandfromwhichdatacanbereadagainwhenneededThisdatacanbereadbackfromthememoryinanysequencedesired,andnotnecessarilythesameorderwhichitwaswritten,hencetheexpressionrandomaccessmemory.AnothertypeofROM(ReadOnlyMemory)isusedtoholdfixedpatternsofinformationwhichcannotbeaffectedbythemicroprocessor;thesepatternsarenotlostwhenpowerisremovedandarenormallyusedtoholdtheProgramwhichdefinesthebehaviorofamicroprocessorbasedsystem.ROMscanbereadlikeRAMs,butunlikeRAMstheycannotbeusedtostorevariableinformation.SomeROMshavetheirdatapatternsputinduringmanufacture,whileothersareprogrammablebytheuserbymeansofspecialequipmentandarecalledProgrammableROMs.ThewidelyusedprogrammableROMsareerasablebymeansofspecialultravioletLampsandarereferredtoasEPROMs,shortforErasableProgrammableReadOnlyMemories.OthernewtypesofdevicecanbeerasedelectricallywithouttheneedforultravioletMemory(RAM,ROM)Micro-ProcessorInput/Output英文翻译-31ight,whicharecalledElectricallyErasableProgrammableReadOnlyMemories,ERPROMs.Themicroprocessorprocessesdataunderthecontroloftheprogram,controllingtheHowofinformationtoandfrommemoryandinput/outputdevices.Someinput/outputdevicesaregeneral-purposetypeswhileothersaredesignedforconktrol1ingspecialhardwaresuchasdiscdrivesorcontrollinginformationtransmissiontoothercomputers.MosttypesofI/0devicesareProgrammabletosomeextent,allowingdifferentmodesofoperation,whilesomeactuallycontainspecial-purposemicroprocesstopermitquitecomplexoperationtobecarriedoutwithoutdirectlyinvolvingthemainmicroprocessor.Themicroprocessor,memoryandinput/outputcircuitmayallbecontainedonthesameintegratedcircuitprovidedthattheapplicationdoesnotrequiretoomuchprogramofdatastorage.Thisisusuallythecaseinlow-costapplicationsuchasthecontrollersusedinmicrowaveovensandautomaticwashingmachines.TheuseofsinglepackageallowsconsiderableseverablecostsavingstobemadewhenarticlesaremanufacturedinlargequantitiesAstechnologydevelops,moreandmorepowerfulprocessorsandlargerandlargeramountsofmemoryarebeingincorporatedintosinglechipmicrocomputerswithresultingsavinginassemblycostsinthefinalproducts.Fortheforeseeablefuture,however,itwillcontinuetobenecessarytointerconnectanumberofintegratedcircuitstomakeamicrocomputerwheneverlargeramountsofstorageorinput/outputarerequired.Anothermajorengineeringapplicationofmicrocomputersisinprocesscontrol.Herethepresenceofthemicrocomputerisusuallymoreapparenttotheuserbecauseprovisionisnormallymadeforprogrammingthemicrocomputerfortheparticularapplication.Inprocesscontrolapplicationsthebenefitsoffittingtheentiresystemontoasinglechipareusuallyoutweighedbythehighdesigncostinvolved,becausethissortofequipmentisproducedinsmallerquantities.Moreover,processcontrollersareusuallymorecomplicatedsothatitismoredifficulttomakethemassingleintegratedcircuits.Twoapproachesarepossible;thecontrollercanbeimplementedasageneral-purposemicrocomputerratherlikeamorerobustversionofahobbycomputer,orasapackagedsystem,designedforreplacingcontrollersbaseonoldertechnologiessuchaselectromagneticrelays.intheformercasethesystemwouldprobablybeprogrammedinconventionalprogramminglanguage英文翻译-4suchastheonestobeintroducelater,whileintheothercaseaspecial-purposelanguagemightbeused,forexampleonewhichallowedthefunctionofthecontrollertobedescribedintermsofrelayinterconnections.IneithercaseprogramscanbestoredinRAM,whichallowsthemtobealteredtosuitchangesinapplication,butthismakestheoverallsystemvulnerableto1ossofpowerunlessbatteriesareusedtoensurecontinuityofsupply.A1ternativclyprogramscanbestoredinROM,inwhichcasetheyvirtuallybecomepartoftheelectronichardwareandareoftenreferredtoasfirmware.Moresophisticatedprocesscontrollersrequireminicomputersfortheirimplementationalthoughtheuseoflargescaleintegratedcircuitsblursthedistinctionbetweenminiandmicrocomputers.Productsandprocesscontrollerofvariouskindsrepresentthemajorityofpreset-daymicrocomputerapplicators,theexactfiguresdependingononesinterpretationofthewordproduct.Virtuallya11engineeringandscientificusesofmicro-computerscanbeassignedtooneorotherofthesecategories.GeneralElectronicsCircuits1Power-supplyCircuitsMostelectronicequipmentrequiresDCvoltagesforitsoperation.TherecanbeprovidedbybatteriesorinternalpowersuppliesthatconvertalternatingcurrentasavailableatthehomeelectronicoutletintoregulatedDCvoltages.ThefirstelementinaninternalDCpowersupplyisatransformer,whichstepsuporstepsdowntheinputvoltagetoalevelsuitablefortheoperationoftheequipment.Asecondaryfunctionofthetransformeristoprovideelectronicgroundinsulationofthedevicefromthepowerlinetoreducepotentialhazards.Arectifier,normallyadiode,thenfollowsthetransformer.Inthepast,vacuumdiodesandawidevarietyofdifferentmaterialssuchasgermaniumcrystalsorcadmiumsulfidewereemployedinthelow-powerrectifiersusedinelectricequipment.Todaysiliconrectifiersareusedalmostexclusivelybecauseoftheirlowcostandhighreliability.FluctuationsandtipplessuperimposedontherectifiedDCvoltage(noticeableasahuminamalfunctioningaudioamplifier)canbefilteredoutbyacapacitor,thelargerthecapacitor,andthesmallertheamountofrippleinthevoltage.Moreprecisecontrolovervoltageslevelsandripplescanbeachievedbyavoltageregulator,which