Different Models of State Machines - Essay Example

Another possible representation is the State transition table. The mealy model for a state machine is one in which the outputs are a function of both the present state and the input. It is a general model for state machines, and assumes that there are two types of inputs; clock inputs and data inputs.

The clock inputs cause the state transitions and gate'' the outputs, (so the outputs are pulsed'' outputs; i.e., they are valid only when the clock is asserted). The data transitions determine the values of the next states and outputs. Essentially, the clock inputs control the timing of the state transitions and outputs, while the data inputs determine their values. In this model, outputs are associated with the states of the device. In the Moore machine, the outputs are stable for the full time the device is in a given state.

(The outputs are said to be level'' outputs, and are valid even when the clock inputs are not asserted.). Again, there are two types of inputs, clock inputs, and data inputs. In this case, however, the clock inputs only directly enable the state transitions. . In general, we can say that; it is possible to convert any Mealy-type machine into an equivalent Moore-type machine, and vice-versa. First, we must define what we mean by two-state machines being equivalent. Two-state machines are said to be equivalent if they produce the same output for all inputs.

Consequently, to derive an equivalent Moore machine from a Mealy machine, it must be possible to guarantee that the two machines produce the same output after any arbitrary input string has been input. This can be done by splitting all the Mealy states corresponding to different outputs, and ensuring that these states are connected to the next states which correspond to equivalent states in the original Mealy machine.