Sequential Logic Circuits

A sequential circuit consists of logic gates and flip-flops. A flip-flop (ff) is a bistable device that has two outputs. One output indicates the true variable of the output, and the other indicates its complement. Such a device is used to store one bit of information. In concept, a sequential circuit uses logic gates to provide the control functions, and it uses flip-flops to store the digital signals. If the output of an ff changes as soon as its input changes, it is called an asynchronous ff. If the output of an ff changes as its input changes but is controlled by a clock, it is a synchronous ff. An asynchronous ff requires no clock, but a synchronous one does. A synchronous ff has a clock input in addition to its data inputs. Thus, the data inputs and clock input jointly control the timing of the change in its output voltage. By grouping an ordered set of flip-flops, we obtain a register. Thus, a register is used to store many bits where each ff is a one-bit storage cell in a register. The length of a register is the number of bits that can be stored. Precisely, an eight-bit register can store eight bits, a 16-bit register can store 16 bits, and a 32-bit register can store 32 bits. If the output of register A is connected to the input of register B, the presence of a clock at the input can transfer the bits from register A to register B. The bits in register A remain after the operation.