Sequential logic circuit counter11/11/2023 In fact, ring counters can be decoded without the use of logic gates. So if a ring counter is less efficient in the use of flip-flops than a binary counter, why do we still need ring counters? One main reason is because ring counters are much easier to decode. For example, a MOD-8 ring counter requires 8 flip-flops while a MOD-8 binary counter only requires 3 (23 = 8). A MOD-N ring counter will require N flip-flops connected in the arrangement as the diagram above.Ī ring counter requires more flip-flops than a binary counter for the same MOD number. A ring counter can be constructed for any MOD number. The ring counter above functions as a MOD-4 counter since it has four distinct states and each flip-flop output waveform has a frequency equal to one-fourth of the clock frequency. Subsequent pulses will cause the sequence to repeat, hence the name ring counter. At the fourth pulse, the 1 at Q0 is transferred back to Q3, resulting in the 1000 state, which is the initial state. The next pulse produces the 0010 state and the third, 0001. At the first pulse, the 1 shifts from Q3 to Q2 and the counter is in the 0100 state. In the diagram above, assuming a starting state of Q3 = 1 and Q2 = Q1 = Q0 = 0. There is usually only a single 1 circulating in the register, as long as clock pulses are applied. It is essentially a circulating shift register connected so that the last flip-flop shifts its value into the first flip-flop. Ring counters are implemented using shift registers. The term synchronous refers to events that have a fixed time In synchronous counters, the clock input is connected to all of the flip-flops so that they are clocked simultaneously.
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