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1、1外文原文外文原文Microcomputersystemronicsystemsareusedfhinginfmationinthemostgeneralsensethisinfmationmaybetelephoneconversationinstrumentreadacompanysaccountsbutineachcasethesamemaintypeofoperationareinvolved:theprocessingstag
2、etransmissionofinfmation.inconventionalelectronicdesigntheseoperationsarecombinedatthefunctionlevelfexampleacounterwhetherelectronicmechanicalstesthecurrentincrementsitbyoneasrequired.Asystemsuchasanelectronicclockwhiche
3、mployscountershasitsstageprocessingcapabilitiesspreadthroughoutthesystembecauseeachcounterisabletosteprocessnumbers.Presentdaymicroprocessbasedsystemsdepartfromthisconventionalapproachbyseparatingthethreefunctionsofproce
4、ssingstagetransmissionintodifferentsectionofthesystem.ThispartitioningintothreemainfunctionswasdevisedbyVonNeumannduringthe1940swasnotconceivedespeciallyfmicrocomputers.Almosteverycomputerevermadehasbeendesignedwiththiss
5、tructuredespitetheenmousrangeintheirphysicalfmstheyhaveallbeenofessentiallythesamebasicdesign.Inamicroprocessbasedsystemtheprocessingwillbeperfmedinthemicroprocessitself.Thestagewillbebymeansofmemycircuitsthecommunicatio
6、nofinfmationintooutofthesystemwillbebymeansofspecialinputoutput(IO)circuits.Itwouldbeimpossibletoidentifyaparticularpieceofhardwarewhichperfmedthecountinginamicroprocessbasedclockbecausethetimewouldbestedinthememyincreme
7、ntedatregularintervalsbutthemicroprocess.Howeverthesoftwarewhichdefinedthesystemsbehaviwouldcontainsectionsthatperfmedascounters.Theapparentlyratherabstractapproachtothearchitectureofthemicroprocessitsassociatedcircuitsa
8、llowsittobeveryflexibleinusesincethesystemisdefinedalmostentirelysoftware.Thedesignprocessislargelyoneofsoftwareengineeringthesimilarproblemsofconstructionmaintenancewhichoccurinconventionalengineeringareencounteredwhenp
9、roducingsoftware.Thefigure1.1illustrateshowthesethreesectionswithinamicrocomputerareconnectedintermsofthecommunicationofinfmationwithinthemachine.Thesystemiscontrolledbythemicroprocesswhichsupervisesthetransferofinfmatio
10、nbetweenitselfthememyinputoutputsections.Theexternalconnectionsrelatetotherest(thatisthe3flowofinfmationtofrommemyinputoutputdevices.Someinputoutputdevicesaregeneralpurposetypeswhileothersaredesignedfcontrollingspecialha
11、rdwaresuchasdiscdrivescontrollinginfmationtransmissiontoothercomputers.MosttypesofIOdevicesareprogrammabletosomeextentallowingdifferentmodesofoperationwhilesomeactuallycontainspecialpurposemicroprocessstopermitquitecompl
12、exoperationstobecarriedoutwithoutdirectlyinvolvingthemainmicroprocess.Themicroprocessmemyinputoutputcircuitmayallbecontainedonthesameintegratedcircuitprovidedthattheapplicationdoesnotrequiretoomuchprogramdatastage.Thisis
13、usuallythecaseinlowcostapplicationsuchasthecontrollersusedinmicrowaveovensautomaticwashingmachines.Theuseofsinglepackageallowsconsiderablecostsavingstoemadewhenarticlesaremanufacturedinlargequantities.Astechnologydevelop
14、smemepowerfulprocessslargerlargeramountsofmemyarebeingincpatedintosinglechipmicrocomputerswithresultingsavinginassemblycostsinthefinalproducts.Fthefeseeablefuturehoweveritwillcontinuetobenecessarytointerconnectanumberofi
15、ntegratedcircuitstomakeamicrocomputerwheneverlargeramountsofstageinputoutputarerequired.Anothermajengineeringapplicationofmicrocomputersisinprocesscontrol.Herethepresenceofthemicrocomputerisusuallymeapparenttotheuserbeca
16、useprovisionisnmallymadefprogrammingthemicrocomputerftheparticularapplication.Inprocesscontrolapplicationsthebenefitsiffittingtheentiresystemontosinglechipareusuallyoutweighedbythehighdesigncostinvolvedbecausethisstifequ
17、ipmentisproducedinsmallerquantities.Meoverprocesscontrollersareusuallymecomplicatedsothatitismedifficulttomakethemassingleintegratedcircuits.Twoapproachesarepossiblethecontrollercanbeimplementedasageneralpurposemicrocomp
18、uterratherlikeamerobustversionifahobbycomputerasapackagedsystemsignedfreplacingcontrollersbasedonoldertechnologiessuchaselectromagicrelays.Inthefmercasethesystemwouldprobablybeprogrammedinconventionalprogramminglanguages
19、suchastheonesto9beintroducedlaterwhileintheothercaseaspecialpurposelanguagemightbeusedfexampleonewhichallowedthefunctionofthecontrollertobedescribedintermsofrelayinterconnections.IneithercaseprogramscanbestedinRAMwhichal
20、lowsthemtobealteredtosuitchangesinapplicationbutthismakestheoverallsystemvulnerabletolossifpowerunlessbatteriesareusedtoensurecontinuityofsupply.AlternativelyprogramscanbestedinROMinwhichcasetheyvirtuallybecomepartofthee
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