Microcomputers Systems.docx
- 文档编号:23966544
- 上传时间:2023-05-23
- 格式:DOCX
- 页数:9
- 大小:28.72KB
Microcomputers Systems.docx
《Microcomputers Systems.docx》由会员分享,可在线阅读,更多相关《Microcomputers Systems.docx(9页珍藏版)》请在冰豆网上搜索。
MicrocomputersSystems
MicrocomputerSystems
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,butifahighpressureofsomedangerouschemicalistobeindicatedorrecordedseveralhundredfeetfromthepointofmeas
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- Microcomputers Systems