The 74ACT11191 is a synchronous, 4-bit binary reversible up/down counter. A synchronous counting operation is provided by having all flip-flops clocked simultaneously so that the outputs change coincident with each other 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 flip-flops are triggered on a low-to-high-level transition of the clock input if the enable input (CTEN) 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. These counters feature a fully independent clock circuit. Changes at the control inputs (CTEN and D/U) that will modify the operating mode have no effect on the contents of the counter until clocking occurs. The function of the counter will be dictated solely by the condition meeting the stable setup and hold times.