The SN74ALS568A decade counter and ´ALS569A binary counters are programmable, count up or down, and offer both synchronous and asynchronous clearing. All synchronous functions are executed on the positive-going edge of the clock (CLK) input.

The clear function is initiated by applying a low level to either asynchronous clear (ACLR\) or synchronous clear (SCLR\). Asynchronous (direct) clearing overrides all other functions of the device, while synchronous clearing overrides only the other synchronous functions. Data is loaded from the A, B, C, and D inputs by holding load () low during a positive-going clock transition. The counting function is enabled only when enable P (ENP\) and enable T (ENT\) are low and ACLR\, SCLR\, andare high. The up/down (U/D\) input controls the direction of the count. These counters count up when U/D\ is high and count down when U/D\ is low.

A high level at the output-enable () input forces the Q outputs into the high-impedance state, and a low level enables those outputs. Counting is independent of. ENT\ is fed forward to enable the ripple-carry output (RCO\) to produce a low-level pulse while the count is zero (all Q outputs low) when counting down or maximum (9 or 15) when counting up. The clocked carry output (CCO\) produces a low-level pulse for a duration equal to that of the low level of the clock whenis low and the counter is enabled (both ENP\ and ENT\ are low); otherwise, CCO\ is high. CCO\ does not have the glitches commonly associated with a ripple-carry output. Cascading is normally accomplished by connectingor CCO\ of the first counter to ENT\ of the next counter. However, for very high-speed counting,should be used for cascading since CCO\ does not become active until the clock returns to the low level.Read more