In digital circuits a shift register is a group of registers set up in a linear fashion which have their inputs and outputs connected together in such a way that the data is shifted down the line when the circuit is activated.

Types

Shift registers can have a combination of serial and parallel inputs and outputs, including serial-in, parallel-out and parallel-in, serial-out types. There are also types that have both serial and parallel input and types with serial and parallel output. There are also bi-directional shift registers which allow you to vary the direction of the shift register. The serial input and outputs of a register can also be connected together to create a circular shift register. One could also create multi-dimensional shift registers..

Uses

One of the most common uses of a shift register is to convert between serial and parallel interfaces. This is useful as many circuits work on groups of bits in parallel, but serial interfaces are simpler to construct. Shift registers can be used as simple delay circuits. Several bi-directional shift registers could also be connected in parallel for a hardware implementation of a stack.

History

One of the first known examples of a shift register was in the Colossus, a code-breaking machine of the 1940s. It was a five-stage device built of vacuum tubes.

See also

• linear feedback shift register