Modulo 6 Counter Design and Circuit

A modulo 6 (MOD-6) counter circuit, known as divide-by-6 counter, can be made using three D-type flip-flops. The circuit design is such that the counter counts from 0 to 5, and then on the 6th count it automatically resets to begin the count again. Since we are using the sixth count itself to cause a reset, it is unstable.

The trick is to start with a MOD-8 counter and then look for the binary sequence 110, which is 6 in decimal. Since this binary sequence is unique, we look for the sequence of 1’s and feed them into an AND gate. The output from the AND gate is then used to control the RESET function on all three flip-flops. Remember that binary is read from right to left (LSB to MSB), whilst the counter output is left to right. Students are likely to make mistakes here, and end up using the incorrect outputs to feed the AND gate.