Xor-gate-up-down-counter


Posted on Sep 30, 2012

One can transform an ordinary binary counter, such as a 7493, into an up/down counter with mode control by adding XOR gates 7486 to the counter`s outputs. The circuit counts up when the DN/UP line is low and down when the DN/UP line is high. To use the 7493 counter to count out its maximum count length of 0 -15, connect the QA output to the BIN input and apply clock pulses to the A IN input.


Xor-gate-up-down-counter
Click here to download the full size of the above Circuit.

The reset input, when high, inhibits the count inputs and simultaneously returns the outputs Ao through Do to low in the up-count mode or 15 in the down-count mode. For normal counting, the reset input must be low. One can easily cascade this counter by feeding the Qv line to the clock input of a succeeding counter.




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