SDAS211B - DECEMBER 1982 - REVISED DECEMBER 1994
The SN54ALS193 and SN74ALS193A are synchronous, reversible, 4-bit up/down binary counters. Synchronous counting operation is provided by having all flip-flops clocked simultaneously so that the outputs change coincident with each other when so instructed by the steering logic. This mode of operation eliminates the output counting spikes normally associated with asynchronous (ripple-clock) counters.
The outputs of the four flip-flops are triggered on a low-to-high-level transition of either count/clock (UP or DOWN) input. The direction of the count is determined by which count input is pulsed while the other count input is high.
All four counters are fully programmable; that is, each output may be preset to either level by placing a low on the load (LOAD\) input and entering the desired data at the data inputs. The output changes to agree with the data inputs independently of the count pulses. This feature allows the counters to be used as modulo-N dividers by simply modifying the count length with the preset inputs.
A high level applied to the clear (CLR) input forces all outputs to the low level. The clear function is independent of the count and LOAD\ inputs. The UP, DOWN, and LOAD\ inputs are buffered to lower the drive requirement, which significantly reduces the loading on, or current required by, clock drivers, etc., for long parallel words.
These counters are designed to be cascaded without the need for external circuitry. The borrow (BO\) output produces a low-level pulse while the count is zero (all Q outputs low) and the DOWN input is low. Similarily, the carry (CO\) output produces a low-level pulse while the count is 9 or 15 (all Q outputs high) and the UP input is low. The counters can then be easily cascaded by feeding BO\ and CO\ to the count-down and count-up inputs, respectively, of the succeeding counter.
The SN54ALS193 is characterized for operation over the full military temperature range of -55°C to 125°C. The SN74ALS193A is characterized for operation from 0°C to 70°C.
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