Q.What is a sequential logic circuit?

Digital circuits fall into two broad families — combinational and sequential — and knowing the difference is the starting point for the whole study of sequential logic.

A combinational logic circuit produces an output that depends only on the present combination of inputs. It has no memory of what happened before, so the same set of inputs always gives the same output. Logic gates, adders, subtractors, encoders, decoders and multiplexers are all combinational; they can be described completely by a truth table or a Boolean expression. …