Mealy sequential machine:
- If the output of a sequential state machine depends on the present state of flip flop and the external inputs. The generalized form of a Mealy circuit is shown below.
The input combinational circuit which is also called as the next state decoder receives inputs from the outputs of memory elements and from the external inputs.
But the most important point to be noted is that the output combinational circuit $C_2$ (also called as output decoder) receives signals from the output of memory elements as well as the external inputs.
Hence the output of mealy circuit is dependent on the present state of memory elements as well as the external inputs.
In a Mealy circuit, the number of states required to represent a sequential system is less than those required for Moore circuit.
Moore sequential machine:
- The synchronous sequential state machine is called Moore machine if the output depends only on the present state of flip flops. The general form of Moore circuit is shown below.
Note that the most important thing for a Moore circuit is that its output depends only upon the present state of memory elements. The external inputs do not influence the outputs.
The combinational circuit $C_1$ on the input side is sometimes called as the next state decoder. The external inputs and the feedback signals from the memory elements are applied to the combinational circuit.
The outputs of the memory elements are applied to another combinational circuit $C_2$ which is also called as output decoder. The output of Moore machine changes only after the active clock edge.
Also, implementation of a logic function needs more number of states than Mealy circuit.