《微机原理与接口技术》——如何读时序图.pdf

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1、UAHCPE/EE421MicrocomputersWEEK#10UAHInterpretingtheTimingDiagramThe68000ReadCycle2TimingDiagramofaSimpleFlip-FlopIdealizedformofthetimingdiagramUAHActualbehaviorofaDflip-flopDataholdtimeDatasetuptimeMaxtimeforoutputtobecomevalidafterclockAlanClements3GeneralformofthetimingdiagramUAHAnaltern

2、ativeformofthetimingdiagramAlanClements4TheClockUAHAmicroprocessorrequiresaclockthatprovidesastreamoftimingpulsestocontrolitsinternaloperationsA68000memoryaccesstakesaminimumofeightclockstatesnumberedfromclockstateS0toclockstateS7AlanClements5UAHAmemoryaccessbeginsinclockstateS0andendsinsta

3、teS7AlanClements6UAHThemostimportantparameteroftheclockisthedurationofacycle,tCYC.AlanClements7UAHAtthestartofamemoryaccesstheCPUsendstheaddressofthelocationitwishestoreadtothememoryAlanClements8AddressTimingUAHWeareinterestedinwhenthe68000generatesanewaddressforuseinthecurrentmemoryaccessT

4、henextslideshowstherelationshipbetweenthenewaddressandthestateofthe68000sclockAlanClements9UAHInstateS1anewInitially,instateaddressbecomesS0theaddressvalidfortheremainderbuscontainstheofthememoryaccessoldaddressAlanClements10UAHThetimeatwhichthecontentsoftheaddressbuschangecanberelatedtothe

5、edgesoftheclock.AlanClements11AddressTimingUAHLetslookatthesequenceofeventsthatgovernthetimingoftheaddressbusTheoldaddressisremovedinstateS0Theaddressbusisfloatedforashorttime,andtheCPUputsoutanewaddressinstateS1AlanClements12UAHTheoldaddressisremovedinclockstateS0andtheaddressbusfloatedAla

6、nClements13UAHtCLAVThedesignerisinterestedinthepointatwhichtheaddressfirstbecomesvalid.ThispointistCLAVsecondsafterthefallingedgeofS0.AlanClements14UAHThememoryneedstoknowwhentheaddressfromtheCPUisvalid.Anaddressstrobe,AS*,isassertedtoindicatethattheaddressisvalid.AlanClements15AddressandAd

7、dressStrobeUAHWeareinterestedintherelationshipbetweenthetimeatwhichtheaddressisvalidandthetimeatwhichtheaddressstrobe,AS*,isassertedWhenAS*isactive-lowitindicatesthattheaddressisvalidWenowlookatthetimingoftheclock,theaddress,andtheaddressstrobeAlanClemen