State Machines
A state machine is used to make predictable transitions through a sequence of states based on the current state of the machine and the external inputs.
The timing of the machine is controlled by a register and a system clock, and the next state of the machine is determined by a combination of logic gates.
Many state machines plod from one state to the other. Other state machines make transitions based on external input.
The block diagram representation of a digital electronics state machine is as follows:
Reference