Need to build a counter circuit using D-type flip flops [closed]

Question

I can only learn by examples it seems. I feel I've understood my classes well... but I cannot for the life of me decide where to begin, or link my understanding to anything practical right now.

I need to do it using Proteus (or similar software?)

Do I make a 4-bit counter and join them together? How do I make D-flip flops synchronous?

I'm hopelessly lost.

Answer 1

A synchronous counter clocks all the outputs at once (all the flops share a common clock.) This differs from a ripple counter, where the Q out of the previous stage clocks the next one.

To make a synchronous up counter, you need to compute the next (D-inputs) value by taking the present (Q-outputs) value and adding 1. This computation is done by an incrementer. You construct an incrementer from a series of half adders.

So in sum, you need:

• four D flip-flops sharing a common clock
• A 4-bit incrementer (4 half adders) to compute the next value

It is also possible to use JK flops in toggle mode, which simplifies the design somewhat. Example in Falstad These only require that you compute the state where the output bit flips (that is, when the lower-significant bits are all 1’s.) However, the ask is for D flip-flops, so you need to use the more complex logic. (Hint: a D flip-flop can be made into a toggle flop with the addition of an XOR gate.)