Editing Finite-state machine (section)

=== Transducers ===
{{Main|Finite-state transducer}}
[[File:Fsm Moore model door control.svg|thumb|Fig. 6 Transducer FSM: Moore model example]]
[[File:Fsm mealy model door control.svg|thumb|Fig. 7 Transducer FSM: Mealy model example]]

''Transducers'' produce output based on a given input and/or a state using actions. They are used for control applications and in the field of [[computational linguistics]].

In control applications, two types are distinguished:

;[[Moore machine]]: The FSM uses only entry actions, i.e., output depends only on state. The advantage of the Moore model is a simplification of the behaviour. Consider an elevator door. The state machine recognizes two commands: "command_open" and "command_close", which trigger state changes. The entry action (E:) in state "Opening" starts a motor opening the door, the entry action in state "Closing" starts a motor in the other direction closing the door. States "Opened" and "Closed" stop the motor when fully opened or closed. They signal to the outside world (e.g., to other state machines) the situation: "door is open" or "door is closed".

;[[Mealy machine]]: The FSM also uses input actions, i.e., output depends on input and state. The use of a Mealy FSM leads often to a reduction of the number of states. The example in figure 7 shows a Mealy FSM implementing the same behaviour as in the Moore example (the behaviour depends on the implemented FSM execution model and will work, e.g., for [[Virtual finite-state machine|virtual FSM]] but not for [[event-driven finite-state machine|event-driven FSM]]). There are two input actions (I:): "start motor to close the door if command_close arrives" and "start motor in the other direction to open the door if command_open arrives". The "opening" and "closing" intermediate states are not shown.