SN74HC191D

The SN74HC191D is a 4-bit synchronous Up/Down Binary Counter 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 the clock input if the count-enable (CTEN\) input is low. A high at CTEN\ inhibits counting. The direction of the count is determined by the level of the down/up (D/U\) input. When D/U\ is low, the counter counts up and when D/U\ is high, it counts down. It features a fully independent clock circuit. Change at the control (CTEN\ and D/U\) inputs that modifies the operating mode has no effect on the contents of the counter until clocking occurs. The function of the counter is dictated solely by the condition meeting the stable setup and hold times.