Johnson counters are one of the most important applications of shift registers. They are created by connecting multiple flip-flops to one another (such that the output of one flip-flop is the input for another), and by connecting the complement of the output of the last flip-flop to the input of the first flip-flop.
For a mod 6 Johnson counter, 3 flip-flops are required. Recall that the number of flip-flops required for a Johnson counter is half the number of used states for that counter. Since a mod 6 Johnson counter can count up to 6 states, 3 flip flops will be required.
Like a ring counter, a Johnson counter is a synchronous counter, hence the clock needs to be in “ON” state for the state transitions can happen.
Circuit Diagram :
Combining the excitation table and the state table here for convenience.
State Diagram :
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