FSM, State Diagrams, ASM

Finite State Machines (FSM)

• Moore - Shown Below on the Left

  • A finite state machine - outputs depend only on the present state of the machine

• Mealy - Shown Below on the right

  • A finite state machine -outputs depend on the present state AND the present input.

State Table

The state table representation of a sequential circuit consists of three sections labeled present state, next state and output. The present state designates the state of flip-flops before the occurrence of a clock pulse. The next state shows the states of flip-flops after the clock pulse, and the output section lists the value of the output variables during the present state.

NOTE: if you are working with a mealy machine, the table may also include inputs

Below shows an example of a state table

State Diagrams

Sequential circuits can also be represented graphically by a state diagram.

• A State is represented as a circle

• The transition between states is indicated by lines or arcs with arrows that connect States.

• State diagrams look slightly different depending on if the diagram is representing a Moore or Mealy FSM.

• numers on lines or arcs

  • Mealy x/y

    • x is the present input

    • y is the output

  • Moore x

    • x is an input

The figure below shows some example of state diagrams

Algorithmic State Machine (ASM chart)

We can also represent the machine as an ASM chart. Below shows the elements used in an ASM Chart

Below shows some example of a Mealy and Moore ASM chart