A Moore machine's outputs depend only on its current state. A Mealy machine's outputs depend on current state and current inputs. Mealy outputs can respond within a cycle to an input change; Moore outputs naturally describe state-based behavior. Both styles can implement useful controllers.
Worked example
In a serial pattern detector, a Moore design can enter a DETECTED state whose output is one. A Mealy design can assert detection on the transition that receives the final matching bit. The observed output timing differs even if both recognize the same bit pattern.
What to watch for
A combinational Mealy output can glitch or respond to unsynchronized inputs. Moore state decoding can also glitch physically; register outputs when required by the interface.
Try it yourself
If an output equation uses both Q, the state, and input X, which style does it describe?
Answer: A Mealy output. A Moore output equation uses the state alone.
How to study this topic
Begin with named states and a complete transition table. Then choose encodings and derive the logic. Trace inputs over several cycles, checking outputs as well as next states, including reset and unexpected encodings.
Explore related programmes
These recorded programmes are upcoming. This article is general educational content, not a syllabus or course sample.
Digital Electronics