An N-line demultiplexer, a.k.a. a 1-to-N demultiplexer, is used to assign a single input line to one of N output lines.
It performs the opposite job of a multiplexer.
The output line which is used depends on a B-bit selection input where B=ceil(log_{2}N).
Here "ceil" is the ceiling function which returns the smallest integer greater than or equal to its argument.

The demultiplexer can be seen as a decoder which has an enable signal, and to show how, consider
an 8-line demultiplexer with input line `A`

, output lines `X0`

, ..., `X7`

,
and selection bits `S0`

, `S1`

, and `S2`

.
The following table shows how to map the demultiplexer's inputs and outputs to the octal decoder's so that it performs a demultiplex function.

Demultiplexer | Decoder |
---|---|

`Xn` | `Xn` |

`Sn` | `An` |

`A` | `E` |

When simulated with test inputs, the decoder gives the following waveform which matches the specification of the demultiplexer
— the binary code `A2 A1 A0`

is decoded to select one of the `Xn`

lines which then has the same value as the
`E`

input.

Kleitz, W. *Digital Microprocessor Fundamentals. 3rd Edition.* Prentice Hall, 2000.

Mano, M. Morris, and Kime, Charles R. *Logic and Computer Design Fundamentals. 2nd Edition.* Prentice Hall, 2000.

Copyright © 2014 Barry Watson. All rights reserved.