Multiplexer

combinatorial-logic

Definition

Multiplexer

A multiplexer (MUX) is a combinatorial logic circuit used to select one signal from multiple input signals and forward it to a single output line. The selection of the input is controlled by a set of selection lines and control signals.

Example

The following example shows a 4-to-1 multiplexer which has four inputs, $e_0,e_1,e_2,e_3$, two selection lines $S_0,S_1$ and one output $o$.

As the table below shows, the multiplexer selects the input $o=e_i$ with $i$ being the binary word $(S_1{S}_0{)}_2$ obtained from the selection lines.

$S_1$	$S_0$	$a$
0	0	$e_0$
0	1	$e_1$
1	0	$e_2$
1	1	$e_3$

Example: If $S_1=1$ and $S_0=1$, then the multiplexer selects $o=e_3$ since the binary word $(S_1{S}_0)$ is equal to $(11{)}_2$, which is equal to $(3{)}_{10}$ in the decimal system.