Understanding Sequential Circuits

A sequential circuit is an interconnection of flip-flops and gates.As all we know that,gates themselves constitute a combinational circuit,but when included with flip-flops,the overall circuit is classified as the sequential circuit.From the block diagram of the sequential circuit you can see that it consists of a combinational circuit and a number of clocked flip-flops.In general,a sequential circuit can consists of a combinational circuit and any number or type of flip-flops.From the diagram it is very much clear that the combinational circuit receives binary signals from external inputs and from the output of the flip-flops.The outputs of the combinational circuit goes to the external outputs and to the inputs of the flip-flops.

Now if we look at the function of each component in the sequential circuit then the main function of gates is to determine the binary value to be stored in the flip-flops after each clock transition.The output of the flip-flops,in turn,are applied to the combinational circuit inputs and determines circuit behavior.This process demonstrate that the outputs of the sequential circuit are function of both external inputs and present state of the flip-flops.Morever the next state of the flip-flop is a function of the present state and external inputs.Thus,sequential circuit is specified by a time sequence of external inputs,external outputs and internal flip-flop binary states.