Question

Mealy output depends on:

• A. State
• B. State and Input
• C. Input
• D. Previous state

Hint:

Mnemonic:
Mealy \( \implies \) State + Input (More dependency, fewer states).
Moore \( \implies \) Only State (Less dependency, more states).
This is a standard question in state machine design.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks about the dependency of the output in a Mealy-type Finite State Machine (FSM).
Sequential circuits designed as finite state machines are categorized into Mealy and Moore models based on how their outputs are derived.

Step 2: Key Formula or Approach:
Let us define the logic mathematical equations for both models:

• Mealy Machine:
The output \( Y(t) \) at any instant is a function of both the current state \( S(t) \) and the current external input \( X(t) \):
\[ Y(t) = f\big(S(t), X(t)\big) \]
• Moore Machine:
The output \( Y(t) \) depends strictly on the current state \( S(t) \) of the system:
\[ Y(t) = g\big(S(t)\big) \]

Step 3: Detailed Explanation:
Let us compare the structural and operational differences between the two models:

• Mealy Model Characteristics:
Since the output is directly linked to the input, any change in the input line is immediately reflected in the output, even between clock edges. This results in asynchronous spikes or glitches.
Mealy machines generally require fewer states to implement the same logic behavior compared to Moore machines, making them more compact.

• Moore Model Characteristics:
The output is fully synchronized with the clock because state transitions occur only on clock edges. Moore machines are safer to cascade but require more states.

Step 4: Final Answer:
The output of a Mealy machine depends on the present state and the current input.