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74LS161DatasheetGeneralDescriptionThesesynchronous,presettablecountersfeatureaninternalcarrylook-aheadforapplicationinhigh-speedcountingdesigns.TheDM74LS161Aare4-bitbinarycounters.ThecarryoutputisdecodedbymeansofaNORgate,thuspreventingspikesduringthenormalcountingmodeofoperation.Synchronousoperationisprovidedbyhavingallflip-flopsclockedsimultaneouslysothattheoutputschangecoincidentwitheachotherwhensoinstructedbythecount-enableinputsandinternalgating.Thismodeofoperationeliminatestheoutputcountingspikeswhicharenormallyassociatedwithasynchronous(rippleclock)counters.Abufferedclockinputtriggersthefourflip-flopsontherising(positive-going)edgeoftheclockinputwaveform.Thesecountersarefullyprogrammable;thatis,theoutputsmaybepresettoeitherlevel.Aspresettingissynchronous,settingupalowlevelattheloadinputdisablesthecounterandcausestheoutputstoagreewiththesetupdataafterthenextclockpulse,regardlessofthelevelsoftheenableinput.TheclearfunctionfortheDM74LS161Aisasynchronous;andalowlevelattheclearinputsetsallfouroftheflip-flopoutputsLOW,regardlessofthelevelsofclock,load,orenableinputs.(這些同步,預置表計數(shù)器為應用在高速計數(shù)功能內(nèi)部攜帶有預見性的設計。DM74LS161A4比特二進制計數(shù)器。套利或非門的輸出是通過解碼,從而防止在正常峰值計數(shù)的操作模式。同步操作是由所有人字拖時鐘同步,以便輸出變化互相重合時,指示count-enable輸入和內(nèi)部控制。這種模式的操作消除了輸出計數(shù)峰值通常與異步計數(shù)器(波紋時鐘)。一個緩沖時鐘輸入觸發(fā)四人字拖(正向的)邊緣的時鐘輸入波形上升。這些計數(shù)器是完全可編程;也就是說,輸出可以被預設的水平。作為預設定是同步的,建立一個低水平的負載輸入禁用計數(shù)器,使輸出后同意設置數(shù)據(jù)在下一個時鐘脈沖，無論使輸入的水平。DM74LS161A的明確的函數(shù)是異步的,明確的輸入和低水平集的所有四個觸發(fā)器輸出低,無論級別的時鐘,負載,或使輸入。)OrderingCodeOrderNumberPackageNumberPackageDescriptionDM74LS161AMM16A16-LeadSmallOutlineIntegratedCircuit(SOIC),JEDECMS-012,0.150NarrowDM74LS161ANN16E16-LeadPlasticDual-In-LinePackage(PDIP),JEDECMS-001,0.300WideFunctionTable

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RecommendedOperatingConditionsSymbolParameterDM54LS161DM74LS161UnitsMiM\NomMaxMin\NomMaxVCCSupplyVoltage4555547555.25VVIHHighLevelInputVoltage22VVILLowLevelInputVoltage0.70.8VIOHHighLevelOutputCurrent-0.4mAIOLLowLevelOutputCurrent48mAfCLKClockFrequency(Note025025MHzClockFrequency(Note020020MHztWPulseWidth(Note1)Clock206206nsClear209209PulseWidth(Note2)Clock2525nsClear2525tSUSetupTime(Note1)Data208208nsEnableP25172517Load25152515SetupTime(Note2)Data2020nsEnableP3030Load3030tHHoldTime(Note1)Data0b30b3nsOthers0b30b3HoldTime(Note2)Data55nsOthers55tRELClearReleaseTime(Note2020nsClearReleaseTime(Note2)2525nsTAFreeAirOperatingTemperatureb55125070CSwitchingCharacteristicsSymbolParameterFrom(Input)To(Output)RL=2kUnitsSymbolParameterFrom(Input)To(Output)CL=15pFCL=50pFUnits

SymbolParameterFrom(Input)To(Output)MinMaxMinMaxUnitsfMAXMaximumClockFrequency2520MHztPLHPropagationDelayTimeLowtoHighLevelOutputClocktoRippleCarry2530nstPHLPropagationDelayTimeHightoLowLevelOutputClocktoRippleCarry3038nstPLHPropagationDelayTimeLowtoHighLevelOutputClockto加(LoadHigh)2227nstPHLPropagationDelayTimeHightoLowLevelOutputClockto曲(LoadHigh)2738nsPhysical