Dual 4-Bit Decade Counter
General Description
Each of these monolithic circuits contains eight masterslave
flip-flops and additional gating to implement two individual
four-bit counters in a single package. The
DM74LS390 incorporates dual divide-by-two and divideby-
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 DM74LS390 has parallel outputs from each
counter stage so that any submultiple of the input count frequency
is available for system-timing signals.
Features
Dual version of the popular DM74LS90
DM74LS390...individual clocks for A and B flip-flops
provide dual ¸ 2 and ¸ 5 counters
Direct clear for each 4-bit counter
Dual 4-bit version can significantly improve system densities
by reducing counter package count by 50%
Typical maximum count frequency...35 MHz
Buffered outputs reduce possibility of collector commutation
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