Answer:

• Registers are digital circuits which are used to store n bits information in the same time and each bit is stored in a flip-flop. Generally, registers are built with D flip-flops. Registers can also be designed using S-It and J-K flip-flops, and presently they are available in MSI ICs.

SHIFT REGISTER:-

• A shift register is an example of a sequential logic circuit. This logic circuit is most commonly used to store digital data during arithmetic and logical operations. Shift register can be constructed by a group of flip-flops. Each flip-flop can store one bit, so a register composed of n flip-flops can store an n bit number.
• The output of one flip-flop is fed to the next flip-flop as input. All these flip-flops are driven by a common clock and they are set or reset simultaneously. Therefore, data processes sequentially. The storing of one bit of data using a D flip-flop is shown in Fig.

• It is depicted in Fig. that data input D is 1 and clock is applied. Then input data '1' is stored in flip-flop as output of D flip-flop is 1. If input is removed, output will be remaining the same. Similarly, '0' can be stored in a D flip-flop as shown in Fig. The operation of a bi-directional type shift register is also explained.CLASSIFICATION OF SHIFT REGISTER

   

There are four basic types of shift registers, namely,

1. Serial In-Serial Out (SISO),
2. Serial In-Parallel Out (SIPO),
3. Parallel In-Serial Out (PISO), and
4. Parallel In-Parallel Out (PIRO).

1. Serial In-Parallel Out (SIPO) :-

• In Serial In-Parallel Out (SIPO), data is applied at the input of register in serial form and the output can be obtained in parallel form after the completely shifting of data in the register. Figure below shows the serial input data, and then parallel output.

2. Serial In-Serial Out (SISO):- 

• In Serial In-Serial Out (SISO) shift register. data is input in serial form and clock pulses are applied to each flip-flop. After each clock pulse, data moves by one position. The output can be obtained in serial form. In this type of shift register, data moves either in the left or right direction. It is depicted in Fig.below that data inputs in the shift register serially as 1001 and data output from shift register is also done serially.

3. Parallel In—Serial Out (PISO):- 

• In the Parallel In—Serial Out shift register, data is loaded into the shift register in parallel form and the data output can be obtained in serial form as illustrated in Fig. below

4 Parallel In—Parallel Out:-

• In the Parallel In-Parallel Out shill register, data is loaded in parallel form 1 0 0 and the data output will be in parallel. In Fig. below, data input is in parallel form but data output from the shift register is also in parallel form.