Page 99 - Digital Electronics by harish

3.3 Registers

A flip-flop can store only one binary digit. Register is a combination of N flip-flops to
store N bits. For example, an 8-bit register can be used to store a data of 8-bit information.

3.3.1 4-bit Shift register

Shit register is a type of register in which data is shifted from one flip-flop to another flip-
flop for storing and retrieving the information. Depending upon how we enter the data into
the shift register (input) and how we take the data from the shift register (output), shift
registers are classified into four types. They are,

1. Serial IN - Serial OUT (SISO) Shift register
2. Serial IN - Parallel OUT (SIPO) Shift register
3. Parallel IN - Serial OUT (PISO) Shift register
4. Parallel IN - Parallel OUT (PIPO) Shift register

The logic diagram of shift register with all the four functions SISO, SIPO, PISO and
PIPO is shown in figure.

Figure : Shift register

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