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Difference Between Mealy And Moore

When it comes to designing digital circuits for solving a specific problem, the two most common methods used are Mealy and Moore. Both Mealy and Moore are Finite State Machines (FSM) that are used to create sequential circuits. These circuits are capable of executing a set of specific functions based on the inputs provided to them.

Both Mealy and Moore state machines are similar in functionality but differ in the way they generate the output. In this article, we’ll discuss the main difference between Mealy and Moore state machines.

Mealy State Machine

A Mealy state machine is a type of FSM that takes input along with the current state as an input and produces an output based on the current state and input. This output can change based on the transition from one state to another.

The output generated by a Mealy state machine is dependent on both the input and the current state of the system. In other words, the output changes with each transition from one state to another.

Here is an example of a Mealy state machine represented by a state diagram:

In this example, the Mealy state machine has two states, A and B. The input to this state machine is represented by the arrows going into each state, and the output from each state is represented by the label on the transition between states.

Moore State Machine

A Moore state machine is another type of FSM that produces output based only on the current state of the system. Unlike Mealy state machines, these machines are not dependent on input when generating the output.

In a Moore state machine, the output only changes when the state of the system changes. In other words, there is no change in output during the transition from one state to another, as opposed to Mealy machines.

Here is an example of a Moore state machine represented by a state diagram:

In this example, the Moore state machine has two states, A and B. The input to this machine is represented by the arrows going into each state, and the output from each state is represented within the state itself.

Key Differences Between Mealy And Moore State Machines

Now that we understand what Mealy and Moore state machines are, let’s examine the key differences between them.

Output Generation

The most significant difference between Mealy and Moore state machines is how they generate their output. As mentioned earlier, the output generated by Mealy state machines is dependent on both the input and the current state of the system, while the output of Moore state machines depends solely on the current state of the system.

Output Synchronization

Another difference between the two state machines is that the output in Moore state machines is synchronized with the state transition, whereas in Mealy state machines, output changes can occur even before transitioning to a new state.

Number Of States

Moore state machines are generally larger than Mealy state machines, as the former requires more states to achieve the desired output. This is because in Mealy state machines, the output can change with each transition, whereas in Moore state machines, the output changes only when the state changes.

Implementation

The implementation of Mealy and Moore state machines differs slightly. In Mealy state machines, the output is determined by the combination of input and state. In contrast, Moore state machines generate output based on the current state. As a result, Mealy state machines have more flexibility when it comes to output generation.

Conclusion

In summary, both Mealy and Moore state machines are popular Finite State Machines used in designing digital circuits. While they are similar in functionality, they differ in the way they generate output and the synchronization of this output with state transition.

Determining which FSM to use depends on the problem at hand, and each has its advantages and disadvantages, making it important to consider the requirements of the system beforehand. By understanding the key differences between Mealy and Moore state machines, you can better determine which FSM will work better for your project.

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Difference Between Mealy And Moore