SN54ALS169B, SN54AS169A, SN74ALS169B, SN74AS169 ASYNCHRONOUS 4-BIT UP/DOWN BINARY COUNTERS

SDAS125B - MARCH 1984 - REVISED DECEMBER 1994

features

• Fully Synchronous Operation for Counting and Programming
• Internal Carry Look-Ahead Circuitry for Fast Counting
• Carry Output for n-Bit Cascading
• Fully Independent Clock Circuit
• Package Options Include Plastic Small-Outline (D) Packages, Ceramic Chip Carriers (FK), and Standard Plastic (N) and Ceramic (J) 300-mil DIPs

description

These synchronous 4-bit up/down binary presettable countersfeature 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 normallyassociated with asynchronous (ripple-clock) counters. A bufferedclock (CLK) input triggers the four flip-flops on the rising(positive-going) edge of the clock waveform.

These counters are fully programmable; that is, they may be presetto either level. The load-input circuitry allows loading with thecarry-enable output of cascaded counters. Because loading issynchronous, setting up a low level at the load (LOAD\) inputdisables the counter and causes the outputs to agree with the datainputs after the next clock pulse.

The internal carry look-ahead circuitry provides for cascadingcounters for n-bit synchronous application without additional gating. and inputs and a ripple-carry output() areinstrumental in accomplishing this function. Both and must be low to count. Thedirection of 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, itcounts down. is fed forwardto enable . , thus enabled, produces alow-level pulse while the count is zero (all inputs low) countingdown or maximum (15) counting up. This low-level overflowripple-carry pulse can be used to enable successive cascaded stages.Transitions at or are allowed regardless of thelevel of the clock input. All inputs are diode clamped to minimizetransmission-line effects, thereby simplifying system design.

These counters feature a fully independent clock circuit. Changesat control inputs (,, , or U/D\) that 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) is dictated solely by the conditionsmeeting the stable setup and hold times.

The SN54ALS169B and SN54AS169A are characterized for operationover the full military temperature range of -55°C to 125°C.The SN74ALS169B and SN74AS169A are characterized for operation from0°C to 70°C.

View more information about generic part numbers:SN54ALS169B, SN54AS169A, SN74ALS169B, SN74AS169A

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