2_RISC_CISC.ppt

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1、StateMachinesTimingComputerBusComputerPerformanceInstructionSetArchitecturesRISC/CISCMachinesCombinationalvs.SequentialLogicTherearetwotypesof“combination”locks418430155102025Combinational:Successdependsonlyonthevalues,nottheorderinwhichtheyareset.Sequential:Successdependsonthes

2、equenceofvalues(e.g,R-13,L-22,R-3).AComputerisanexampleofaSequentialCircuitInformationStorage:DFlipFlop(DLatch)D

3、Qn+10

4、01

5、1RegisterAregisterstoresamulti-bit(vector)value.WeuseacollectionofD-latches,allcontrolledbyacommonwriteenablepulse,callitWE.WhenthewriteenableWE=1,then-bitval

6、ueDiswrittentoregister.TimingDiagramConventionsBacktoourSequentialLogicThisone.418430155102025Combinational:Successdependsonlyonthevalues,nottheorderinwhichtheyareset.Sequential:Successdependsonthesequenceofvalues(e.g,R-13,L-22,R-3).AFiniteStateMachineCombinationallogicDetermine

7、outputsateachstate.Determinenextstate.StorageelementsMaintainstaterepresentation.StateMachineCombinationalLogicCircuitStorageElementsInputsOutputsClockTheClockFrequently,aclockcircuittriggerstransitionfromonestatetothenext.Atthebeginningofeachclockcycle,thestatemachinemakesatransi

8、tion,basedonthecurrentstateandtheexternalinputs(Synchronous).Notalwaysrequired.Inlockexample,theinputitselftriggersatransition(Asynchronous).“1”“0”timeOneCycleStateThestateofasystemisasnapshotofalltherelevantelementsofthesystematthemomentthesnapshotistaken.FiniteStateMachineAdescr

9、iptionofasystemwiththefollowingcomponents:AfinitenumberofstatesAfinitenumberofexternalinputsAfinitenumberofexternaloutputsAnexplicitspecificationofallstatetransitionsAnexplicitspecificationofwhatdetermineseachexternaloutputvalueOftendescribedbyastatediagram:-Thesetofallpossiblestat

10、es.-Inputsthattriggerstatetransitions.-Outputsassociatedwitheachstate(orwitheachtransition).StateofSequentialLockOurlockexamplehasfourdifferentstates,labelledA-D:A:Thelockisnotopen,andnorelevantoperationshavebeenperformed.B:Thelockisnotopen,andtheuserhascompletedtheR-13operation.C:

11、Thelockisnotopen,andtheuse