Choosing Mealy vs Moore State Machines: Factors & Insights

[EvLer]

What are some possible criteria when to choose Mealy or Moore state machine?
I know that for Mealy, output is a function of present state and input and in Moore it's just present state. I know it also probably depends on the design specifications, but ... just wondering.

Any insights are very much appreciated.

 

[mezarashi]

It's difficult to say in general other than that given definition. It's important to be able to identify how a machine works and knowing whether it is Mealy verus Moore is part of it. For design purposes, you can see that a machine that has output as a function of state only is somewhat 'better' due to its synchronous nature. Moore machines usually have the output and input buffered by some kind of sequential logic (flip-flops and latches), while Mealy machines usually have part of the output directly coming from the input through some combinational logic.

 

[piercas]

I would like to provide some insights on the factors to consider when choosing between Mealy and Moore state machines.

Firstly, it is important to understand the fundamental difference between the two state machines. As you mentioned, in Mealy machines, the output is a function of both the present state and input, while in Moore machines, the output is only dependent on the present state. This difference in output behavior can have significant implications for the overall design and functionality of the state machine.

One of the main criteria to consider when choosing between Mealy and Moore state machines is the complexity of the system. Mealy machines tend to have fewer states and transitions compared to Moore machines, as the output is dependent on both the present state and input. This can be advantageous for systems with limited resources or strict timing constraints. However, Moore machines offer a more straightforward and predictable output behavior, making them suitable for systems that require precise and deterministic outputs.

Another factor to consider is the type of input and output signals. Mealy machines are more suitable for systems with fast-changing inputs and outputs, as the output can be updated immediately based on the input. On the other hand, Moore machines are better suited for systems with slow-changing inputs and outputs, as the output is only updated when the state changes.

The design specifications of the system also play a crucial role in determining which state machine to choose. Mealy machines are more flexible and can handle a wider range of inputs and outputs compared to Moore machines. Therefore, if the system requires a high level of flexibility and adaptability, Mealy machines may be the better choice.

In conclusion, the choice between Mealy and Moore state machines ultimately depends on the specific requirements and constraints of the system. It is essential to carefully evaluate the complexity, input/output behavior, and design specifications of the system to make an informed decision.