SDFS056A - D2932, MARCH 1987 - REVISED OCTOBER 1993
This synchronous, presettable, 4-bit binary counter features aninternal carry look-ahead circuitry for application in high-speedcounting designs. Synchronous operation is provided by having allflip-flops clocked simultaneously so that the outputs changecoincident with each other when so instructed by the count-enable(ENP, ENT) inputs and internal gating. This mode of operationeliminates the output counting spikes that are normally associatedwith asynchronous (ripple-clock) counters; however, counting spikesmay occur on the ripple-carry (RCO) output. A buffered clock (CLK)input triggers the four flip-flops on the rising (positive-going)edge of the clock input waveform.
This counter is fully programmable; that is, it may be preset toany number between 0 and 15. As presetting is synchronous, setting upa low level at the load (
)input disables the counter and causes the outputs to agree with thesetup data after the next clock pulse regardless of the levels of theenable inputs.
The clear function for the SN74F161A is asynchronous and a lowlevel at the clear (
)input sets all four of the flip-flop outputs low regardless of thelevels of the clock, load, or enable inputs.
The carry look-ahead circuitry provides for cascading counters forn-bit synchronous applications without additional gating.Instrumental in accomplishing this function are two count-enable(ENP, ENT) inputs and a ripple-carry (RCO) output. Both ENP and ENTmust be high to count, and ENT if fed forward to enable RCO. RCO thusenabled will produce a high-level pulse while the count is 15 (HHHH).The high-level overflow ripple-carry pulse can be used to enablesuccessive cascaded stages. Transitions at ENP or ENT are allowedregardless of the level of the clock input.
The SN74F161A features a fully independent clock circuit. Changesat control inputs (ENP, ENT, or) that will modify the operating mode have no effect onthe contents of the counter until clocking occurs. The function ofthe counter (whether enabled, disabled, loading, or counting) will bedictated solely by the conditions meeting the setup and hold times.
The SN74F161A is characterized for operation from 0°C to70°C.
View more information about generic part numbers:SN74F161A
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