DM74LS191 Synchronous 4-Bit Up/Down Counter with Mode Control August 1986 Revised February 1999 DM74LS191 Synchronous 4-Bit Up/Down Counter with Mode Control General Description The DM74LS191 circuit is a synchronous, reversible, up/ down counter.
Synchronous operation is provided by having all flip-flops clocked simultaneously, so that the outputs change simultaneously 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 master-slave flip-flops are triggered on a LOW-to-HIGH level transition of the clock input, if the enable input is LOW.
A HIGH at the e...

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