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1、原文：ThisdesigntakeatMCS-51monolithicintegratedcircuitasthecorefullusehardwaresourcedesign'sonekindoffrequencymeter,thisfrequencymeterwillbemeasuredfirstthatsignalenlargementreshapingprocessing,turnssatisfiesTTL/whichthemonolithicintegratedcircuitI/OmouthacceptstheC
2、MOScompatiblesignalfrommonolithicintegratedcircuit'sT1inputportinputdirectsummationpulsenumber,themonolithicintegratedcircuitinteriortimerfixedtimeis1S,bynowaccumulatedthepulsenumbernamelyforismeasuredthesignalthefrequency.Finallypassesthroughmonolithicintegratedc
3、ircuitprocessingtodelivertothelcdliquidcrystaldisplaymonitordemonstration.CentralProcessingUnitDesignsTheCPUisthekeycomponentofadigitalcomputer.Itspurposeistodecodeinstructionreceivedfrommemoryandperformtransfers,arithmetic,logic,andcontroloperationswithdatastored
4、ininternalregisters,memory,orI/Ointerfaceunits.Externally,theCPUprovidesoneormorebusesfortransferringinstructions,data,andcontrolinformationtoandfromcomponentsconnectedtoit.Inthegenericcomputeratthebeginningofchapter1,theCPUisapartoftheprocessorandisheavilyshaded.
5、CPUs,however,mayalsoappearincomputers.Small,relativelysimplecomputerscalledmicrocontrollersareusedincomputersandinotherdigitalsystemstoperformlimitedorspecializedtasks.Forexample,amicrocontrollerispresentinthekeyboardandinthemonitorinthegenericcomputer;thus,thesec
6、omponentsarealsoshaded.Insuchmicrocontrollers,theCPUmaybequitedifferentfromthosediscussedinthischapter.Thewordlengthsmaybeshort(say,fouroreightbits),thenumberofregisterssmall,andtheinstructionsetslimited.Performance,relativelyspeaking,ispoor,butadequateforthetask.
7、Mostimportant,thecostofthesemicrocontrollersisverylow,makingtheirusecosteffective.Inthefollowingpages,weconsidertwocomputerCPUs,oneforacomplexinstructionsetcomputer(CISC)andtheotherforareducedinstructionsetcomputer(RISC).Afteradetailedexaminationofthedesigns,wecom
8、paretheperformanceofthetwoCPUsandpresentabriefoverviewofsomemethodsusedtoenhancethatperformance.Finally,werelatethedesignideasdiscussedtogeneraldigitals
