Part Number: 74LS191
Function: Synchronous 4-Bit Up/Down Counters With Up/Down Mode Control
Pakcage : DIP, SOP 16 Pin
Manufacturer: Texas Instruments
The 74LS191 is Synchronous 4-Bit Up/Down Counter.
The ‘190, ‘LS190, ‘191, and ‘LS191 are synchronous, reversible up/down counters having a complexity of 8 equivalent gates. The SN191 and SN74LS191 are 4-bit binary counters and the SN74190 and SN74LS190 are BCD counters. Synchronous 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 master-slave flip-flops are triggered on a low-to-high transition of the clock input if the enable input is low. A high at the enable input inhibits counting. Level changes at the enable input should be made only when the clock input is high. The direction of the count is determined by the level of the down/up input. When low, the counter count up and when high, it counts down. A false clock may occur if the down/up input changes while the clock is low. A false ripple carry may occur if both the clock and enable are low and the down/up input is high during a load pulse.
Logic Symbols :
1. Counts 8-4-2-1 BCD or Binary
2. Single Down/Up Count Control Line
3. Count Enable Control Input
4. Ripple Clock Output for Cascading
5. Asynchronously Presettable with Load Control
6. Parallel Outputs
7. Cascadable for n-Bit Applications