This counter has an unusual design. Instead of using toggle flip-flops, this counter uses an adder and a register. The output of the adder leads back to one of its inputs, while being delayed by a register. The adder also makes it possible to count by any number that you want, from 0 to F.
The four logic sources on the left side are for controlling what number to count by. It is set to count by 3's once you start the simulation.
