10 Difference Between Mealy And Moore Machine

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What Is Mealy Machine?

In the theory of computation, a Mealy machine is a finite-state machine whose output values are determined both by its current state and the current inputs.

Mealy machine can be described by a 6 tuple (Q, δ, Ʃ, O, X, q0 ) where:

  • Q is a finite set of states.
  • Ʃ is a finite set of symbols referred to as the input alphabets.
  • δ is the input transition function where δ:Q x Ʃ ―>Q
  • O is a finite set of symbols referred to as output alphabet.
  • X is the output transition function where X:Q x Ʃ―>O
  • q0 is the initial state from where any input is processed (q0 ϵQ)

What You Need To Know About Mealy Machine

  1. Mealy machine changes its output based on its current input and present state.
  2. Mealy machine will have same or fewer states than Moore machine.
  3. Output is placed on transition.
  4. The value of the output function is a function of the transitions and the changes, when the input logic on the present state is done.
  5. Mealy machines react faster to inputs. They generally react in the same clock cycle.
  6. Asynchronous output generation through the state changes synchronous to the clock.
  7. Generally requires fewer states for synthesis.
  8. Requires less hardware to design.
  9. A counter is not a Mealy machine.
  10. Not necessarily easy to design.

What Is Moore Machine?

In the theory of computation, a Moore machine is a finite-state machine whose output values are determined only by its current state. A Moore machine can be described as by a 6 tuple (Q, δ, Ʃ, O, X, q0 ) where:

  • Q is a finite set of states.
  • Ʃ is a finite set of symbols referred to as the input alphabets.
  • δ is the input transition function where δ:Q x Ʃ ―>Q
  • O is a finite set of symbols referred to as output alphabet.
  • X is the output transition function where X:Q x Ʃ―>O
  • q0 is the initial state from where any input is processed (q0 ϵQ)

What You Need To Know About Moore Machine

  1. Output of Moore machine only depends on its current state and not on the current input.
  2. Generally, it has more states than Mealy machine.
  3. Output is placed on transition.
  4. The value of the output function is a function of the current state and the changes at the clock edges, whenever state changes occur.
  5. In Moore machines, more logic is required to decode the output resulting in more circuit delays. They generally react one clock cycle later.
  6. Both output and state change synchronous to the clock edge.
  7. Generally requires more states for synthesis.
  8. More hardware is required to design.
  9. A counter is a Moore machine.
  10. Easy to design.

Difference Between Mealy And Moore Machine  In Tabular Form

BASIS OF COMPARISON MEALY MACHINE MOORE MACHINE
Description Mealy machine changes its output based on its current input and present state.   Output of Moore machine only depends on its current state and not on the current input.  
States Mealy machine will have same or fewer states than Moore machine.   It has more states than Mealy machine.  
Output Output is placed on transition.   Output is placed on transition.  
Value Of Output Function The value of the output function is a function of the transitions and the changes, when the input logic on the present state is done.   The value of the output function is a function of the current state and the changes at the clock edges, whenever state changes occur.  
Reaction To Inputs Mealy machines react faster to inputs. They generally react in the same clock cycle.   More logic is required to decode the output resulting in more circuit delays. They generally react one clock cycle later.
Output And State Asynchronous output generation through the state changes synchronous to the clock.   Both output and state change synchronous to the clock edge.  
States Requirement Generally requires fewer states for synthesis.   Generally requires more states for synthesis.  
Hardware Requirement Requires less hardware to design.   More hardware is required to design.  
Counter A counter is not a Mealy machine.   A counter is a Moore machine.  
Design Not necessarily easy to design.   Easy to design.