Each of these monolithic circuits contains eight master-slave flip-flops
and additional gating to implement two individual four-bit counters in a single
package. The '390 and 'LS390 incorporate dual divide-by-two and divide-by-five
counters, which can be used to implement cycle lengths equal to any whole
and/or cumulative multiples of 2 and/or 5 up to divide-by-100. When connected
as a bi-quinary counter, the separate divide-by-two circuit can be used to
provide symmetry (a square wave) at the final output stage. The '393 and 'LS393
each comprise two independent four-bit binary counters each having a clear
and a clock input. N-bit binary counters can be implemented with each package
providing the capability of divide-by-256. The '390, 'LS390, '393, and 'LS393
have parallel outputs from each counter stage so that any submultiple of the
input count frequency is available for system-timing signals. Series 54 and
Series 54LS circuits are characterized for operation over the full military
temperature range of -55°C to 125°C; Series 74 and Series 74LS circuits
are characterized for operation from 0°C to 70°C.
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