SN74F169 SYNCHRONOUS 4-BIT UP/DOWN BINARY COUNTER

SDFS089 - MARCH 1987 - REVISED OCTOBER 1993

features

• Fully Synchronous Operation for Counting and Programming
• Internal Look-Ahead Circuitry for Fast Counting
• Carry Output for N-Bit Cascading
• Fully Independent Clock Circuit
• Package Options Include Plastic Small-Outline Packages and Standard Plastic 300-mil DIPs

description

This synchronous, presettable, 4-bit up/down binary counterfeatures an internal carry look-ahead circuitry for cascading inhigh-speed counting applications. Synchronous operation is providedby having all flip-flops clocked simultaneously so that the outputschange coincident with each other when so instructed by thecount-enable (, inputs and internal gating. Thismode of operation eliminates the output counting spikes that arenormally associated with asynchronous (ripple-clock) counters. Abuffered clock (CLK) input triggers the four flip-flops on the rising(positive-going) edge of the clock waveform.

This counter is fully programmable; that is, it may be preset toany number between 0 and its maximum count. The load-input circuitryallows loading with the carry-enable output of cascaded counters. Asloading is synchronous, setting up a low level at the load () input disables the counter andcauses the outputs to agree with the data inputs after the next clockpulse.

The carry look-ahead circuitry provides for cascading counters forn-bit synchronous application without additional gating. Instrumentalin accomplishing this function are two count-enable (, ) inputs and a ripple-carry () output. Both and must be low to count. The directionof the count is determined by the level of the up/down (U/D\) input.When U/D\ is high, the counter counts up; when low, it counts down.Input is fed forwardto enable the . thus enabled will produce alow-level pulse while the count is zero (all inputs low) countingdown or maximum (9 or 15) counting up. This low-level overflowripple-carry pulse can be used to enable successive cascaded stages.Transitions at or are allowed regardless of the levelof the clock input. All inputs are diode clamped to minimizetransmission-line effects, thereby simplifying system design.

The SN74F169 features a fully independent clock circuit. Changesat control inputs (,, or U/D\) that will modify theoperating mode have no effect on the contents of the counter untilclocking occurs. The function of the counter (whether enabled,disabled, loading, or counting) will be dictated solely by theconditions meeting the setup and hold times.

The SN74F169 is characterized for operation from 0°C to70°C.

View more information about generic part numbers:SN74F169

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