A register is simply a group of flip flop that can be used to store a binary number. Each flip flop is capable of storing one bit information. A register capable of shifting its binary information in one or more directions is called a shift register.
The logical configuration or shift register consists of a chain of flip flops in cascade with the output of one flip flop connected to the input of the next flip flop. All the flip flop receive common clock pulses which activated the shift from one stage to the next. The flip flops used to construct register are usually either JK or D types.
Thus, shift registers are important digital building blocks which stores binary data. They are used as sequential logic circuits as are constructed from flip flops. They are used as temporary memories and for shifting data. They are also used for changing data format. They can be used to want number of pulses entering into a system.
There are four basic types of registers. They are:
i. Serial in- serial out shift register
It is a type of register that can be loaded with data serially and has only one serial output. Usually edge triggered JK, SR or D flip flop are used to construct such registers.
ii. serial in - parallel out shift register
It is a type of register that can be loaded with data serially and has parallel, it is simply necessary to have all the data bits available as outputs at the same time. This is easily accomplished by connecting the output of each flip flop to an output pin. It is constructed by using RS flip flops having clock inputs that are sensitive to NTs.
iii. Parallel in - serial out shift register
It is a type of register that can be loaded with parallel data and has one serial output. A single clock transition loads the data into the register in parallel when the control is low. Again when the control is high, clock transitions will shift the data through the register serially.
iv. Parallel in -parallel out shift register
It is a type of register that can be loaded with parallel data and has parallel outputs available. It is simply used to store data and is sometimes called a data register, or data latch. It is not appropriate for shifting data.
This note is derived from MSC physics, Nepal.