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Figure 55: A 4-bit binary asynchronous up counter time diagram
16.4 A 4-bit Asynchronous binary down counter
Figure 56: Down counter circuit diagram
n
A down counter counts from a predefined value to zero. The predefined value (2 -1) is determined by
the number of flip flops in the counter, for example if the number of flip flops (n) is four (4) then the
down counter would count from 15 to 0.
The down counter in figure 56 operates as follows:
The J and K inputs of all the flip flops are tied to a binary 1 (5v), so all the flip flops are ready to toggle
the present state as and when a clock pulse is applied. But the flip flops cannot toggle simultaneously
since the clock is connected in serial and FF1 cannot change its state before FF0 changes its present
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