4-bit bidirectional shift register with parallel load

Bidirectional Shift Register:

A register that can shift in both directions called a bi-directional shift register. Some shift registers provide the necessary input and output terminals for parallel transfer. The most general shift register has all the capabilities listed below. Others may have some of these capabilities, with at least one shift operation.

1. An input for clock pulses to synchronize all operations.
2. A shift-right operation and a serial input line associated with the shift-right.
3. A shift-left operation and a serial input line associated with the shift-left.
4. A parallel load operation and n input lines associated with the parallel transfer.
5. n-parallel output lines.
6. A control state that leaves the information in the register unchanged even though clock pulses are applied continuously.

4-bit Bidirectional Shift Register:

A 4-bit bidirectional shift register with parallel load is shown below figure:

Each stage consists of a D flip-flop and a 4 x 1 multiplexer. The two selection inputs 51 and 50 select one of the multiplexer data inputs for the D flip-flop. The selection lines control the mode of operation of the register according to the function table shown below Table. When the mode control 5150 = 00, data input 0 of each multiplexer is selected. This condition forms a path from the output of each flip-flop to the input of the same flip-flop. The next clock transition transfers into each flip-flop the binary value it held previously, and no change of state occurs.