SHIFT REGISTERS

In a shift register the flip-flops are connected in series.The output of each flip-flop is connected to the input of the adjacent flip-flop.The contents of a shift register can be shifted within the register without changing the order of the bits.Data are shifted one position left or right at a time when one clock pulse is applied.shift registers are used for the temporary storage of data.They are used where bit shifting is required for manipulating,computing or processing data.They are ideally suited to processing serial data,converting serial data to parallel data,and converting parallel data to serial data,converting parallel data to serial data.They can be built using D,J-K or R-S flip-flops.Depending upon the modes of loading and reading out the data there are four types of shift-registers:

(i)serial-in,serial-out

(ii)serial-in,parallel-out

(iii)parallel-in,serial-out

(iv)parallel-in,parallel-out.

Example of shift register ICs are:

(i)7491 8-bit serial-in,serial-out shift registers.

(ii)74164 8-bit serial-in,parallel-out shift registers.

(iii)74165and74166 8-bit serial/parallel-in,serial-out shift registers.

(iv)74198 8-bit bidirectional universal shift registers.

(v)74199 8-bit serial/parallel-in,parallel-out shift reisters.

Universal shift registers are provide with mode select pins for I/O data transfer.