Sequential logic is a form of binary circuit design that employs one or more inputs and one or more outputs, whose states are related by defined rules that depend, in part, on previous states. Each of the inputs and output(s) can attain either of two states: logic 0 (low) or logic 1 (high).
A common example of a circuit employing sequential logic is the flip-flop, also called a bistable gate. A simple flip-flop has two stable states. The flip-flop maintains its states indefinitely until an input pulse called a trigger is received. If a trigger is received, the flip-flop outputs change their states according to defined rules, and remain in those states until another trigger is received.
There are several different kinds of flip-flop circuits, with designators such as D, T, J-K, and R-S. Flip-flop circuits are interconnected to form the logic gates that comprise digital integrated circuits ( IC s) such as memory chips and microprocessors.
Sequential logic differs from combinatorial logic (also called combinational logic). In the latter scheme, the output states depend only on the input states at a specific moment in time, and not on previous states.