74HC191D (NEXPERIA)

The 74HC191D is a presettable synchronous 4-bit binary Up/Down Counter, pin compatible with low power Schottky TTL (LSTTL). It is asynchronously presettable 4-bit binary up/down counters. They contain four master/slave flip-flops with internal gating and steering logic to provide asynchronous preset and synchronous count-up and count-down operation. Asynchronous parallel load capability permits the counter to be preset to any desired number. Information present on the parallel data inputs (D0 to D3) is loaded into the counter and appears on the outputs when the parallel load (PL) input is low. Counting is inhibited by a HIGH level on the count enable (CE) input. When CE is low internal state changes are initiated synchronously by the low-to-high transition of the clock input. The up/down (U/D) input signal determines the direction of counting. The CE input may go low when the clock is in either state, however, the low-to-high CE transition must occur only when the clock is high.