CHAPTER 4 The Components of the System 2.ppt

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1、CHAPTER4TheComponentsoftheSystemUnitProcessorFundamentalConceptsProcessorfetchesoneinstructionatatimeandperformtheoperationspecified.Instructionsarefetchedfromsuccessivememorylocationsuntilabranchorajumpinstructionisencountered.Processorkeepstrackoftheaddressoft

2、hememorylocationcontainingthenextinstructiontobefetchedusingProgramCounter(PC).InstructionRegister(IR)ExecutinganInstructionFetchthecontentsofthememorylocationpointedtobythePC.ThecontentsofthislocationareloadedintotheIR(fetchphase).IR←[[PC]]Assumingthatthememory

3、isbyteaddressable,incrementthecontentsofthePCby4(fetchphase).PC←[PC]+4CarryouttheactionsspecifiedbytheinstructionintheIR(executionphase).InternalorganizationoftheprocessorALURegistersfortemporarystorageVariousdigitalcircuitsforexecutingdifferentmicrooperations.(

4、gates,MUX,decoders,counters).InternalpathformovementofdatabetweenALUandregisters.Drivercircuitsfortransmittingsignalstoexternalunits.Receivercircuitsforincomingsignalsfromexternalunits.PC:KeepstrackofexecutionofaprogramContainsthememoryaddressofthenextinstructio

5、ntobefetchedandexecuted.MAR:Holdstheaddressofthelocationtobeaccessed.I/PofMARisconnectedtoInternalbusandanO/ptoexternalbus.MDR:Containsdatatobewrittenintoorreadoutoftheaddressedlocation.IThas2inputsand2Outputs.DatacanbeloadedintoMDReitherfrommemorybusorfrominter

6、nalprocessorbus.ThedataandaddresslinesareconnectedtotheinternalbusviaMDRandMARALU:Usedtoperformarithmeticandlogicaloperation.DataPath:Theregisters,ALUandinterconnectingbusarecollectivelyreferredtoasthedatapath.Registers:TheprocessorregistersR0toRn-1varyconsidera

7、blyfromoneprocessortoanother.Registersareprovidedforgeneralpurposeusedbyprogrammer.Specialpurposeregisters-index&stackregisters.RegistersY,Z&TEMParetemporaryregistersusedbyprocessorduringtheexecutionofsomeinstruction.Multiplexer:Selecteithertheoutputoftheregiste

8、rYoraconstantvalue4tobeprovidedasinputAoftheALU.Constant4isusedbytheprocessortoincrementthecontentsofPC.Datatransferbetweentworegisters:EX:TransferthecontentsofR1toR4