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Introduction to Finite State Machines (FSM)

Digital Logic Systems: From Zero to Hero

49. Introduction to Finite State Machines (FSM)

Sequential circuits that exhibit specific behaviors based on a well-defined sequence of states are modeled using Finite State Machines (FSMs). FSMs are the abstract model for most digital control logic.

Components of an FSM

  1. States: The current values stored in the memory elements (FFs).
  2. Inputs: External signals that trigger transitions.
  3. Outputs: Signals generated based on the state and/or input.
  4. Transitions: The rules defining how the machine moves from one state to the next.

Types of FSMs

1. Mealy Model

The output is a function of both the current state AND the current input. This means the output can change immediately upon an input change, even if the state hasn't changed yet.

2. Moore Model

The output is a function of the current state ONLY. The output changes only after a clock edge causes a state transition.

FSM Design Process

Designing a control circuit using FSM involves:

  1. Creating the State Diagram (visual representation).
  2. Creating the State Table (tabular representation).
  3. Selecting Flip-Flop types (D, JK).
  4. Minimizing excitation logic (using K-Maps or Q-M).

This systematic approach allows for the creation of complex controllers used in CPUs, traffic lights, and communication protocols.