Johnson Counter

A Johnson counter is a modified ring counter, where the inverted output from the last flip flop is connected to the input to the first. The register cycles through a sequence of bit-patterns. The MOD of the Johnson counter is 2n if n flip-flops are used. The main advantage of the Johnson counter counter is that it only needs half the number of flip-flops compared to the standard ring counter for the same MOD.

It can be implemented using D-type flip-flops (or JK-type flip-flops).

Notes:
• Enable the flip-flops by clicking the RESET (Green) switch. The RESET switch is a on/off switch (similar to a room light switch)
• Click on CLK (Red) switch and observe the changes in the outputs of the flip flops. The CLK switch is a momentary switch (similar to a door bell switch - normally off).
• The D flip flop clock has a rising edge CLK input. For example Q₁ behaves as follows:
  • The D input value just before the CLK rising edge is noted (Q₀).
  • When CLK rising edge occurs, Q₁ is assigned the previously noted D value (Q₀).
  
• The MOD or number of unique states of this 3 flip flop johnson counter is 6.

Truth Table
State	Q0	Q1	Q2
0	0	0	0
1	1	0	0
2	1	1	0
3	1	1	1
4	0	1	1
5	0	0	1

• Simulate and Breadboard the Johnson Counter circuit.