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Explain Mealy and Moore sequential machine

Mumbai University > ELECTRO > Sem 3 > Digital Circuits and Designs

Marks: 7M

Year: May2015 , Dec2013

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## 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.