Introduction to Sequential Systems

The systems that have been discussed so far have been purely combinational. The fundamental property of such systems is that, at all times, all of the outputs are determined solely by the present instantaneous values of all the inputs. Of course, in a practical system, there will be some delay between an input change and the resulting changes in one or more of the outputs; but, when equilibrium is reached, a knowledge of all the inputs, together with the logical structure of the system itself, enables all of the outputs to be determined uniquely. In contrast, the outputs of sequential systems are determined not only by the present values of the inputs but also by their previous values.