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1、无锡职业技术学院毕业设计说明书（中英文翻译）FoundationofPLC1.ThecentralprocessingunitAlthoughreferredtoasthebrainofthesystem,theCentralProcessingUnitinanormalinstallationistheunsunghero,buriedinacontrolcabinet,allbutforgotten.2.BasicFunctionalityInaprogrammablecontrollersystem,thecentralprocessingunit(CPU)providesboththe
2、heartandthebrainrequiredforsuccessfulandtimelycontrolexecution.Itrapidlyandefficientlyscansallofthesysteminputs,examinesandsolvestheapplicationlogic,andupdatesallofthesystemoutputs.Inaddition,italsogivesitselfacheckupeachscantoensurethatitsstructureisstillintact.Inthischapterwewillexaminethecentralp
3、rocessingunitasitrelatestotheentiresystem.IncludedwillbethevariousfunctionalblocksintheCPU,typicalscantechniques,I/Ointerfaceandmemoryusers,powersupplies,andsystemdiagnostics.3.TypicalFunctionBlockInteractionsInpractice,thecentralprocessingunitcanvaryinitsarchitecture,butconsistsofthebasicbuildingbl
4、ockstructureillustratedinFig.1.1.Theprocessingsectionconsistsofoneormoremicroprocessorsandtheirassociatedcircuitry.Whileitistruethatsomeoftheluxuryofusingmicroprocessors,mostmodernsystemsuseeitherasinglemicroprocessorssuchastheAMD2903,usedinabitslicearchitecture.Thismultiplemicroprocessorsystemtobre
5、akthecontrolsystemtasksintomanysmallcomponentswhichcanbeexecutedinparallel.Theresultofthisapproachistoachieveexecutionspeedsthatareordersofmagnitudefasterthantheirsingle-taskingcounterparts.InadditiontoefficientlyprocessingdirectI/Ocontrolinformationandbeingprogrammable,therealadvantagethatmicroproc
6、essor-basedsystemhaveovertheirhardwiredrelaycounterpartsistheabilitytoacquireandmanipulatenumericaldataeasily.Itisthisattributethatmakesprogrammablecontrollersthepowerhousesthattheyaretodayinsolvingtoughfactoryautomationproblems.Thefactoryoftomorrowwillrunefficientlyonlyifqualityinformationaboutproc
7、essneedsandstatusoftheprocessequipmentareknownonarealtimesbasis.Thiscanandwillcomeaboutonlyiftheunitlevelcontrollers,includingprogrammablecontrollers,areempoweredwiththeabilitytocollect,analyze,concen
