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1、CHAPTER4TheComponentsoftheSystemUnitProcessorFundamentalConceptsProcessorfetchesoneinstructionatatimeandperformtheoperationspecified.Instructionsarefetchedfromsuccessivememorylocationsuntilabranchorajumpinstructionisencountered.Processorkeepstrackoftheaddressoftheme
2、morylocationcontainingthenextinstructiontobefetchedusingProgramCounter(PC).InstructionRegister(IR)ExecutinganInstructionFetchthecontentsofthememorylocationpointedtobythePC.ThecontentsofthislocationareloadedintotheIR(fetchphase).IR←[[PC]]Assumingthatthememoryisbytead
3、dressable,incrementthecontentsofthePCby4(fetchphase).PC←[PC]+4CarryouttheactionsspecifiedbytheinstructionintheIR(executionphase).InternalorganizationoftheprocessorALURegistersfortemporarystorageVariousdigitalcircuitsforexecutingdifferentmicrooperations.(gates,MUX,de
4、coders,counters).InternalpathformovementofdatabetweenALUandregisters.Drivercircuitsfortransmittingsignalstoexternalunits.Receivercircuitsforincomingsignalsfromexternalunits.PC:KeepstrackofexecutionofaprogramContainsthememoryaddressofthenextinstructiontobefetchedande
5、xecuted.MAR:Holdstheaddressofthelocationtobeaccessed.I/PofMARisconnectedtoInternalbusandanO/ptoexternalbus.MDR:Containsdatatobewrittenintoorreadoutoftheaddressedlocation.IThas2inputsand2Outputs.DatacanbeloadedintoMDReitherfrommemorybusorfrominternalprocessorbus.Thed
6、ataandaddresslinesareconnectedtotheinternalbusviaMDRandMARALU:Usedtoperformarithmeticandlogicaloperation.DataPath:Theregisters,ALUandinterconnectingbusarecollectivelyreferredtoasthedatapath.Registers:TheprocessorregistersR0toRn-1varyconsiderablyfromoneprocessortoano
7、ther.Registersareprovidedforgeneralpurposeusedbyprogrammer.Specialpurposeregisters-index&stackregisters.RegistersY,Z&TEMParetemporaryregistersusedbyprocessorduringtheexecutionofsomeinstruction.Multiplexer:SelecteithertheoutputoftheregisterYoraconstantvalue4tobeprovi
8、dedasinputAoftheALU.Constant4isusedbytheprocessortoincrementthecontentsofPC.Datatransferbetweentworegisters:EX:TransferthecontentsofR1toR4
