SYNCHRONOUS SEQUENTIAL CIRCUIT
This type of system uses storage elements called flip-flops that are employed to change their binary value only at discrete instants of time. Synchronous sequential circuits use logic gates and flip-flop storage devices. Sequential circuits have a clock signal as one of their inputs. All state transitions in such circuits occur only when the clock value is either 0 or 1 or happen at the rising or falling edges of the clock depending on the type of memory elements used in the circuit. Synchronization is achieved by a timing device called a clock pulse generator. Clock pulses are distributed throughout the system in such a way that the flip-flops are affected only with the arrival of the synchronization pulse. Synchronous sequential circuits that use clock pulses in the inputs are called clocked-sequential circuits. They are stable and their timing can easily be broken down into independent discrete steps, each of which is considered separately.
A clock signal is a periodic square wave that indefinitely switches from 0 to 1 and from 1 to 0 at fixed intervals. Clock cycle time or clock period: the time interval between two consecutive rising or falling edges of the clock.
Clock Frequency = 1 / clock cycle time (measured in cycles per second or Hz)
Example: Clock cycle time = 10ns clock frequency = 100M