The 'ALS193A 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 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 () 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
i nputs. The
UP, DOWN, and inputs are
buffered to lower the drive requirement, which significantly reduces
the loading on, or current required by, clock drivers, etc., for long
These counters are designed to be cascaded without the need for
external circuitry. The borrow () 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 and to the
count-down and count-up inputs, respectively, of the succeeding
The SN54ALS193A 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
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