Zoë Blade's notebook

Shift register

A shift register is essentially an array of binary bits. It can receive clock pulses, and each time it does, all its bits are nudged along one position. The bit on one end is transferred to the array's output, while its neighbouring bit is moved to replace it, and so on, with the bit on the other end being replaced by the array's input.

It achieves a similar effect to a bucket brigade device, except it's digital, dealing only with Boolean values. It's made from an array of flipflops feeding into each other.

By connecting the individual bits to additional inputs and outputs, a shift register can do various useful things, such as convert serial data (a series of single bits) into parallel data (a series of whole grouped words of bits) or vice versa.

By using XOR logic gates to modify some of these bits before feeding them back into the input in a feedback loop, it's possible to make a decent approximation of white noise. This is how a digital noise generator works, as used in the TR-909.[1]


  1. "A Look at the TR-909's Noise Generator" Tom Wiltshire, Electric Druid, 2019

Types of electronic component: Shift register