In Sequential circuits output is a function of present inputs and pat output. These circuits have a feedback element or memory element which stores the output of the circuit and makes it available at the input. The following is the general diagram of sequential circuits:
The binary information stored in the memory element that is fed back into the circuit defines the state of the circuit. Sequential circuits are of two types:
Synchronous circuits: In these types of circuit, output is defined only on the basis of values of inputs at discrete instants of time. In these circuits we use flip-flops as memory devices and a common clock is used to control the working of the circuit. A clock is a periodic wave which continuously changes its state from 1 to 0 and 0 to 1 as
When-ever pulse goes from high to low, it is called FALLING or TRAILING EDGE and when pulse goes from low to high, it is called RISING EDGE.
Asynchronous circuits: In these types of circuit every change in the inputs affects output and output depends on values at every instant of the inputs. All the circuits which don’t have any flip-flops or clock are called Asynchronous circuits. Hence all the combinational circuits are Asynchronous circuits.