The ’HC193 devices are 4-bit synchronous, reversible, up/down binary counters. Synchronous operation is provided by having all flip-flops clocked simultaneously so that the outputs change coincidentally 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 either count (clock) input (UP or DOWN). The direction of counting is determined by which count input is pulsed while the other count input is high.
All four counters are fully programmable; that is, each output may be preset to either level by placing a low on the load (LOAD) input and entering the desired data at the data inputs. The output changes to agree with the data inputs independently of the count pulses. This feature allows the counters to be used as modulo-N dividers simply by modifying the count length with the preset inputs.
A clear (CLR) input has been provided that forces all outputs to the low level when a high level is applied. The clear function is independent of the count and LOAD(overline) inputs.
These counters were designed to be cascaded without the need for external circuitry. The borrow (BO(overline)) output produces a low-level pulse while the count is zero (all outputs low) and DOWN is low. Similarly, the carry (CO(overline)) output produces a low-level pulse while the count is maximum (9 or 15), and UP is low. The counters then can be cascaded easily by feeding BO(overline) and CO(overline) to DOWN and UP, respectively, of the succeeding counter.
TI SN74HC193DR