Mealy vs. Moore Machine: Key Differences, Timing & Best Use Cases
Mealy Machine outputs depend on the current state and the input signal; Moore Machine outputs hinge solely on the current state, making it one step later.
Engineers often confuse them because timing diagrams look alike until a sudden input glitch hits—then the Mealy reacts instantly, Moore waits, and the scope trace tells the story.
Key Differences
Mealy: output changes with input transition → fewer states, faster reaction, risk of transient glitches. Moore: output tied to state → larger state table, predictable timing, easier to verify.
Which One Should You Choose?
Need low latency traffic lights or UART baud generators? Pick Mealy. Want clean, glitch-free elevator control or vending-machine logic? Moore’s steadier output wins.
Examples and Daily Life
Think smartphone haptic feedback (Mealy: buzz on each key-press) versus elevator arrival chime (Moore: ding once the door-state is reached).
Can I mix both styles in one design?
Absolutely—many FPGAs blend Mealy paths for speed-critical blocks and Moore for stable outputs.
Which is easier to test formally?
Moore, because output depends only on state, so assertions ignore input timing chaos.