Sequential circuits are a class of digital circuits in which the output values depends not only on the input values but also on the past * state* of the circuit. This circuits utilize storage elements that store the values of logic signals.

There are two approaches when designing sequential circuits:

  • Moore type
    Circuits whose outputs depend only on the state of the circuit are called of Moore type
  • Mealy type
    Circuits whose outputs depend on both the state and the primary inputs are called Mealy type

These circuits can be represented in a more abstract way by finite state machines.