HD74HC191

HD74HC190/HD74HC191 Synchronous Up/Down Decade Counter (Single Clock Line) Synchronous Up/Donw 4-bit Binary Counter (Single Clock Line) Description The HD74HC190 and HD74HC191 are synchronous, reverside up/down counters. The HD74HC190 is a 4-bit decade counter and the HD74HC191 is a 4-bit binary counter. 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 G input is low. A high at Enable G 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 (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. These counters are fully programmable; that is, the outputs may each be preset to either level by placing a low on the load input and entering the desired data at the data inputs. The output will change to agree with the data inputs independ...