In our daily life we used register to store information. For same purpose in digital electronics world a shift register is used.Now we discuss on What is a shift register in digital electronics ?
Register is a group of binary storage cells capable of holding binary information. Now depending upon the size of information, a group of flip flops constitutes a register, since each flip flop can store single bit information. And in same manner n-bit registers, has n number of flip flops. And it is capable of holding n-bits of information. In addition to flip flops a register can have a combinational part that performs data-processing tasks.
Various types of shift registers are available in MSI circuits of digital world. A shift register may be build combination of flip flop and input gates. The simplest possible register is one that contains no external gates, and is constructed of only flip flops. In bellow figure shows such a type of register constructed of four SR flip flops, with a common clock pulse input.
The clock pulse enables all the flip flops at the same instant so that the information available at the four inputs can be transferred into the 4 bit shift register. All the flip flops in a shift register should respond to the clock pulse transition. Hence they should be either of the edge-triggered type or the master-slave type. A group of flip flops sensitive to the pulse duration is commonly called a gated latch. Latches are suitable to temporarily store binary information that is to be transferred to an external destination. They should not be used in the design of sequential circuits that have feedback connections.
Now as we discussed regarding different type of shift register then depending upon the input output operation we can categories them in four types those are
- Serial in/Serial out (SISO)
- Serial in/Parallel out (SIPO)
- Parallel in/Serial out (PISO)
- Parallel in/Parallel out (PIPO).