Logic trainer kit, J-K Flip-flop IC - 7476 wires.
Logic trainer kit, D Flip-flop IC - 7474 wires.
The Johnson counter is a modification of ring counter. In this the inverted output of the last stage flip flop is connected to the input of first flip flop. If we use n flip flops to design the Johnson counter, it is known as 2n bit Johnson counter or Mod 2n Johnson counter. This is an advantage of the Johnson counter that it requires only half number of flip flops that of a ring counter uses, to design the same Mod. The main difference between the 4 bit ring counter and the Johnson counter is that is in ring counter, we connect the output of last flip flop directly to the input of first flip flop. But in Johnson counter, we connect the inverted output of last stage to the first stage input. The Johnson counter is also known as Twisted Ring Counter, with a feedback. In Johnson counter the input of the first flip flop is connected from the inverted output of the last flip flop. The Johnson counter or switch trail ring counter is designed in such a way that it overcomes the limitations of ring counter. Mainly it reduces the number of flip flops required for designing the circuit.
CLock Pulse No | FFA | FFB | FFC | FFD |
1 | 1/ | 0 | 0 | 0 |
2 | 1 | 1 | 0 | 0 |
3 | 1 | 1 | 1 | 0 |
4 | 1 | 1 | 1 | 1 |
5 | 0 | 1 | 1 | 1 |
6 | 0 | 0 | 1 | 1 |
7 | 0 | 0 | 0 | 1 |
Thus the Johnson counter was designed and their truth table is verified.
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