ABSTRACT
In a combinational circuit shown in Fig. 2.1, the input at any instant is totally determined by the presents inputs. This indicates that for every change of input there is immediate change in the output. However, there are some occasions when we wish the output not to change, once set, when there is a change in the input combination. This basically gives the idea of sequential circuits. A digital logic circuit is said to be a sequential logic circuit if it consists of memory elements in addition to the combinational circuit. Moreover, the outputs of the circuit at any instant of time will depend upon the present input as well as the present state of the memory elements. Figure 2.2 represents a sequential circuit that contains a combinational circuit to which memory element are connected to from a feedback path. The function of the memory is to store binary information at any given instant representing the states of the sequential circuit. The sequential circuit generates the binary output determined by the received binary input together with the present state of memory element. To store binary information, we can use a circuit called flip-flop, which is the basic memory element in digital systems.
