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

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

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

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

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.

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

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.

Serial in/parallel out shift registers 4-bit register

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.

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

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

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

4-bit parallel in/serial out

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

Parallel In/Parallel Out Shift Registers 4-bit version

Parallel In/Parallel Out Shift Registers 4-bit version

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

Bidirectional 4-bit Shift Register

Bidirectional 4-bit Shift Register

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