Ring 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 output of the last flip-flop to the input of the first flip-flop.
For a mod 2 ring counter, two flip-flops will be required. Recall that the number of states that can be counted by a ring counter is equal to the number of flip-flops being used. Since a mod 2 ring counter can count up to 2 states, 2 flip-flops will be required.
Since a ring counter is a synchronous counter, the clock needs to be in “ON” state so that state transitions can happen and the ring counter can function normally.
Circuit Diagram :
From the diagram, we can see that D1 = Q0 and D0 = Q1
Combining the excitation table and the state table here for convenience.
State Diagram :
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