单片机外文文献翻译Word文档下载推荐.docx
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单片机外文文献翻译Word文档下载推荐.docx
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Electronicsystemsareusedforhandinginformationinthemostgeneralsense;
thisinformationmaybetelephoneconversation,instrumentreadoracompany’saccounts,butineachcasethesamemaintypeofoperationareinvolved:
theprocessing,storageandtransmissionofinformation.inconventionalelectronicdesigntheseoperationsarecombinedatthefunctionlevel;
forexampleacounter,whetherelectronicormechanical,storesthecurrentandincrementsitbyoneasrequired.Asystemsuchasanelectronicclockwhichemployscountershasitsstorageandprocessingcapabilitiesspreadthroughoutthesystembecauseeachcounterisabletostoreandprocessnumbers.
Presentdaymicroprocessorbasedsystemsdepartfromthisconventionalapproachbyseparatingthethreefunctionsofprocessing,storage,andtransmissionintodifferentsectionofthesystem.ThispartitioningintothreemainfunctionswasdevisedbyVonNeumannduringthe1940s,andwasnotconceivedespeciallyformicrocomputers.Almosteverycomputerevermadehasbeendesignedwiththisstructure,anddespitetheenormousrangeintheirphysicalforms,theyhaveallbeenofessentiallythesamebasicdesign.
Inamicroprocessorbasedsystemtheprocessingwillbeperformedinthemicroprocessoritself.Thestoragewillbebymeansofmemorycircuitsandthecommunicationofinformationintoandoutofthesystemwillbebymeansofspecialinput/output(I/O)circuits.Itwouldbeimpossibletoidentifyaparticularpieceofhardwarewhichperformedthecountinginamicroprocessorbasedclockbecausethetimewouldbestoredinthememoryandincrementedatregularintervalsbutthemicroprocessor.However,thesoftwarewhichdefinedthesystem’sbehaviorwouldcontainsectionsthatperformedascounters.Theapparentlyratherabstractapproachtothearchitectureofthemicroprocessoranditsassociatedcircuitsallowsittobeveryflexibleinuse,sincethesystemisdefinedalmostentirelysoftware.Thedesignprocessislargelyoneofsoftwareengineering,andthesimilarproblemsofconstructionandmaintenancewhichoccurinconventionalengineeringareencounteredwhenproducingsoftware.
Thefigure1.1illustrateshowthesethreesectionswithinamicrocomputerareconnectedintermsofthecommunicationofinformationwithinthemachine.Thesystemiscontrolledbythemicroprocessorwhichsupervisesthetransferofinformationbetweenitselfandthememoryandinput/outputsections.Theexternalconnectionsrelatetotherest(thatis,thenon-computerpart)oftheengineeringsystem.
Fig.1.1ThreeSectionsofaTypicalMicrocomputer
Althoughonlyonestoragesectionhasbeenshowninthediagram,inpracticetwodistincttypesofmemoryRAMandROMareused.Ineachcase,theword‘memory’isratherinappropriatesinceacomputersmemoryismorelikeafilingcabinetinconcept;
informationisstoredinasetofnumbered‘boxes’anditisreferencedbytheserialnumberofthe‘box’inquestion.
MicrocomputersuseRAM(RandomAccessMemory)intowhichdatacanbewrittenandfromwhichdatacanbereadagainwhenneeded.Thisdatacanbereadbackfromthememoryinanysequencedesired,andnotnecessarilythesameorderinwhichitwaswritten,hencetheexpression‘random’accessmemory.AnothertypeofROM(ReadOnlyMemory)isusedtoholdfixedpatternsofinformationwhichcannotbeaffectedbythemicroprocessor;
thesepatternsarenotlostwhenpowerisremovedandarenormallyusedtoholdtheprogramwhichdefinesthebehaviorofamicroprocessorbasedsystem.ROMscanbereadlikeRAMs,butunlikeRAMstheycannotbeusedtostorevariableinformation.SomeROMshavetheirdatapatternsputinduringmanufacture,whileothersareprogrammablebytheuserbymeansofspecialequipmentandarecalledprogrammableROMs.ThewidelyusedprogrammableROMsareerasablebymeansofspecialultravioletlampsandarereferredtoasEPROMs,shortforErasableProgrammableReadOnlyMemories.Othernewtypesofdevicecanbeerasedelectricallywithouttheneedforultravioletlight,whicharecalledElectricallyErasableProgrammableReadOnlyMemories,EEPROMs.
Themicroprocessorprocessesdataunderthecontroloftheprogram,controllingtheflowofinformationtoandfrommemoryandinput/outputdevices.Someinput/outputdevicesaregeneral-purposetypeswhileothersaredesignedforcontrollingspecialhardwaresuchasdiscdrivesorcontrollinginformationtransmissiontoothercomputers.MosttypesofI/Odevicesareprogrammabletosomeextent,allowingdifferentmodesofoperation,whilesomeactuallycontainspecial-purposemicroprocessorstopermitquitecomplexoperationstobecarriedoutwithoutdirectlyinvolvingthemainmicroprocessor.
Themicroprocessorprocessesdataunderthecontroloftheprogram,controllingtheflowofinformationtoandfrommemoryandinput/outputdevices.Someinput/outputdevicesaregeneral-purposetypeswhileothersaredesignedforcontrollingspecialhardwaresuchasdiscdrivesorcontrollinginformationtransmissiontoothercomputers.MosttypesofI/Odevicesareprogrammabletosomeextent,allowingdifferentmodesofoperation,whilesomeactuallycontainspecial-purposemicroprocessorstopermitquitecomplexoperationstobecarriedoutwithoutdirectlyinvolvingthemainmicroprocessor.
Themicroprocessor,memoryandinput/outputcircuitmayallbecontainedonthesameintegratedcircuitprovidedthattheapplicationdoesnotrequiretoomuchprogramordatastorage.Thisisusuallythecaseinlow-costapplicationsuchasthecontrollersusedinmicrowaveovensandautomaticwashingmachines.Theuseofsinglepackageallowsconsiderablecostsavingstoemadewhenarticlesaremanufacturedinlargequantities.Astechnologydevelops,moreandmorepowerfulprocessorsandlargerandlargeramountsofmemoryarebeingincorporatedintosinglechipmicrocomputerswithresultingsavinginassemblycostsinthefinalproducts.Fortheforeseeablefuture,however,itwillcontinuetobenecessarytointerconnectanumberofintegratedcircuitstomakeamicrocomputerwheneverlargeramountsofstorageorinput/outputarerequired.
Anothermajorengineeringapplicationofmicrocomputersisinprocesscontrol.Herethepresenceofthemicrocomputerisusuallymoreapparenttotheuserbecauseprovisionisnormallymadeforprogrammingthemicrocomputerfortheparticularapplication.Inprocesscontrolapplicationsthebenefitslffittingtheentiresystemontosinglechipareusuallyoutweighedbythehighdesigncostinvolved,becausethissortlfequipmentisproducedinsmallerquantities.Moreover,processcontrollersareusuallymorecomplicatedsothatitismoredifficulttomakethemassingleintegratedcircuits.Twoapproachesarepossible;
thecontrollercanbeimplementedasageneral-purposemicrocomputerratherlikeamorerobustversionlfahobbycomputer,orasa‘packaged’system,signedforreplacingcontrollersbasedonoldertechnologiessuchaselectromagneticrelays.Intheformercasethesystemwouldprobablybeprogrammedinconventionalprogramminglanguagessuchastheonesto9beintroducedlater,whileintheothercaseaspecial-purposelanguagemightbeused,forexampleonewhichallowedthefunctionofthecontrollertobedescribedintermsofrelayinterconnections,IneithercaseprogramscanbestoredinRAM,whichallowsthemtobealteredtosuitchangesinapplication,butthismakestheoverallsystemvulnerabletolosslfpowerunlessbatteriesareusedtoensurecontinuityofsupply.AlternativelyprogramscanbestoredinROM,inwhichcasetheyvirtuallybecomepartoftheelectronic‘hardware’andareoftenreferredtoasfirmware.Moresophisticatedprocesscontrollersrequireminicomputersfortheirimplementation,althoughtheuselflargescaleintegratedcircuits‘thedistinctionbetweenminiandmicrocomputers,Productsandprocesscontrollersofvariouskindsrepresentthemajorityofpresent-daymicrocomputerapplications,theexactfiguresdependingonone’sinterpretationoftheword‘product’.Virtuallyallengineeringandscientificusesofmicrocomputerscanbeassignedtooneorotherofthesecategories.ButinthesystemwemoststudyPressureandPressureTransmitters.Pressureariseswhenaforceisappliedoveranarea.ProvidedtheforceisoneNewtonanduniformlyovertheareaofonesquaremeters,thepressurehasbeendesignatedonePascal.Pressureisauniversalprocessingcondition.Itisalsoaconditionoflifeontheplanet:
weliveatthebottomofanatmosphericoceanthatextendsupwardformanymiles.Thismassofairhasweight,andthisweightpressingdownwardcausesatmosphericpressure.Water,afundamentalnecessityoflife,issuppliedtomostofusunderpressure.Inthetypicalprocessplant,pressureinfluencesboilingpointtemperatures,condensingpointtemperatures,processefficiency,costs,andotherimportantfactors.Themeasurementandcontrolofpressureorlackofit-vacuum-inthetypicalprocessplantiscritical.
Theworkinginstrumentsintheplantusuallyincludesimplepressuregauges,precisionrecordersandindicators,andpneumaticandelectronicpressuretransmitters.Apressuretransmittermakesapressuremeasurementandgenerateseitherapneumaticorelectricalsignaloutputthatisproportionaltothepressurebeingsensed.
Intheprocessplant,itisimpracticaltolocatethecontrolinstrumentsoutintheplaceneartheprocess.Itisalsotruethatmostmeasurementsarenoteasilytransmittedfromsomeremotelocation.Pressuremeasurementisanexception,butifahighpressureofsomedangerouschemicalistobeindicatedorrecordedseveralhundredfeetfromthepointofmeasurement,a
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