74393

74393  Dual 4-bit (0-15) ripple counter

 

The 74393 contains two separate 4-bit (0 to 15) counters, one on each side of the chip. They are ripple counters so beware that glitches may occur in logic systems connected to their outputs due to the slight delay before the later outputs respond to a clock pulse.

The count advances as the clock input becomes low (on the falling-edge), this is indicated by the bar over the clock label. This is the usual clock behaviour of ripple counters and it means means a counter output can directly drive the clock input of the next counter in a chain.

For normal operation the reset input should be low, making it high resets the counter to zero (0000, QA-QD low).

Counting to less than 15 can be achieved by connecting the appropriate output(s) to the reset input, using an AND gate if necessary. For example to count 0 to 8 connect QA (1) and QD (8) to reset using an AND gate.

The 74393 contains two separate 4-bit (0 to 15) counters, one on each side of the chip. They are ripple counters so beware that glitches may occur in logic systems connected to their outputs due to the slight delay before the later outputs respond to a clock pulse.

The count advances as the clock input becomes low (on the falling-edge), this is indicated by the bar over the clock label. This is the usual clock behaviour of ripple counters and it means means a counter output can directly drive the clock input of the next counter in a chain.

For normal operation the reset input should be low, making it high resets the counter to zero (0000, QA-QD low).

Counting to less than 15 can be achieved by connecting the appropriate output(s) to the reset input, using an AND gate if necessary. For example to count 0 to 8 connect QA (1) and QD (8) to reset using an AND gate.

Connecting ripple counters in a chain
The diagram below shows how to link ripple counters in a chain, notice how the highest output QD of each counter drives the clock input of the next counter.