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Sequential Circuits

Synchronous Counter

In synchronous counters we have the same clock signal to all the flip-flops.

MOD-4 Synchronous counter: We discuss here a 2-bit synchronous counter. We have the circuit for this as:s

We have the initial outputs as Q0=0 & Q1=0. Whenever the first negative clock edge comes O/P of 1st FF becomes 1 as we have J & K for 1st FF as 1 and hence output of 1st FF toggles and changes from 0 to 1. But when 1st cock edge had come output of 1st FF was 0. Hence J & K for 2nd FF for 1st edge are 0. So output of this FF doesn’t change and we get Q1=0. so the output is (Q1Q0)2= 012.

On the next edge, output of 1st FF changes from 1 to 0 as J & K are always 1 for this FF. Inputs for 2nd edge for 2nd FF are J=1 & K=1. Hence output changes from 0 to 1. so we get the count as (Q1Q0)2= 102.

Similarly on the next edge we’ll get the output count as (Q1Q0)2= 112.

And on the 4th clock edge both the outputs get reset and we get the output as (Q1Q0)2= 002 and again whole procedure is repeated.

We’ll be studying other synchronous counter when we discuss the design of synchronous circuits later.

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