- A single 7474 IC consist of 2 flip flops so you need two 7474 ICs for implementing Johnson counter.
- Initially all the flip flops are cleared, so the time inverted output (Q’) of 3rd flip flop is high or logic 1.
- This logic 1 is appears at the input of 1st flip flop. During the first clock pulse this logic 1 is transferred to the output of 1st flip flop. Thus the total output of Johnson counter is 100.
- Then input of 1st and 2nd flip flop is logic 1 and after the second clock pulse these inputs appear at the outputs of 1st and 2nd flip flop. So the total output is 110.
- Similarly for the next clock pulse, the output will be 111.
- During this state (111) the time inverted output (Q’) is logic 0. This 0 is fed to the 1st flip flop. Then the 0 will circulate through the flip flops as 011,001,000.