1. Shift Registers Dr. Rebhi S. Baraka rbaraka@iugaza.edu
Logic Design (CSCI 2301)
Department of Computer Science
Faculty of Information Technology
The Islamic University of Gaza

2. Outline Basic shift register functions
Serial in/serial out shift registers
Serial in/parallel out shift registers
Parallel in/serial out shift registers
Parallel in/parallel out shift registers
Bidirectional shift registers

3. Basic shift register functions
A register is a digital circuit with basic functions:
Data storage and
Data movement
The storage capacity of a register is the total number of bits it can retain.
Shift registers consists of an arrangement of flips-flops
Each stage (flip-flop) in a shift register represents one bit of storage capacity.
The shifting capacity permits the movement of data from stage to stage within the register or into or out of the register upon application of clock pulses.
The basic difference between a register and a counter is that a register has no specified sequence of states, except in certain very specialized applications.
A register is used solely for storing and shifting data

4. Serial in/serial out shift registers
It accepts data serially, one bit at a time on a single line, and produces the sorted information on its output also in a serial form

5. Serial in/serial out shift registers
4 bit register
It needs 4 clock pulses to store 4 bits
Example:
Illustrate entry of the 4 bits 1010 into the register.
Illustrate serially shifting the 4 bits out of the register, i.e. clearing the register.

6. Example: Show the states of the 5-bit shift register for the specified data input and clock waveforms. The registered is initially cleared.

7. Serial in/parallel out shift registers
Data bits are entered serially as illustrated before
Once the data are stored, the output of each stage is available on its output line.

8. Serial in/parallel out shift registers
4-bit register

9. Serial in/parallel out shift registers
Example: Show the state of the 4-bit register foe the data input and clock waveforms. The register initially contains all 1s.

10. Serial In/Parallel Out Shift Registers
8-bit serial in/parallel out

11. Parallel In/Serial Out Shift Registers
The bits are entered simultaneously into their respective stages.
The serial output appears bit by bit per clock pulse.
To store 4 bits, we need 1 clock pulse
To shift them out them, we need another 3 clock pulses.
4-bit parallel in/serial out

12. Parallel In/Serial Out Shift Registers
4-bit parallel in/serial out

13. 4-bit parallel in/serial out

14. Parallel In/Parallel Out Shift Registers
The bits are entered simultaneously into their respective stages.
Immediately, the bits appear on the parallel outputs.
4-bit version

15. Parallel In/Parallel Out Shift Registers
4-bit version

16. Parallel In/Parallel Out Shift Registers
4-bit version

17. Bidirectional Shift Register
A bidirectional shift register is one in which the data can be shifted either left or right.
4-bit version

18. Bidirectional 4-bit Shift Register

19. Bidirectional 4-bit Shift Register

20. End of the slides