Pulse and Digital Circuits

18.7 MODULUS COUNTERS

A counter can shorten its modulus by the non-utilization of all the possible states. Here, the non-utilization states are bypassed with suitable feedback. If the number of utilized states are N, then it is Mod-N counter. For example, a Mod-5 counter utilizes 5 states. Using n flip-flops we can get 2ⁿ states. Therefore, if a Mod-5 counter is required, we need to have a counter which can count 2³, i.e., 8 states so that we can skip 3 states. The number of flip-flops required here are 3. From the state diagram we can see that the counter goes through the states 000 to 100 and skips the states 101, 110 and 111. These states are considered as the don’t care states.

EXAMPLE

Example 18.5: Design a Mod-5 counter.

Solution:

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