Multiplexers

Multiplexers

A multiplexer, sometimes referred to as a MUX, is a device that uses a set of control inputs to select which of several data inputs is to be connected to a single data output. With n binary “select lines,” one of 2n data inputs can be connected to the output.

Image below presents a block diagram of a multiplexer with three select lines, S2, S1, and S0, and eight data lines, D0 through D7.

Multiplexer divides one high-speed communication circuit into several lower speed circuits (for the primary reason of saving communication line cost) which allows many devices to use it simultaneously.

A multiplexer acts like a television channel selector. All of the stations are broadcast constantly to the television’s input, but only the channel that has been selected is displayed. As for the eight-channel multiplexer in image above, its operation can be described with the truth table shown below,

For example, if the selector inputs are set to S2 = 0, S1 = 1, and S0 = 1, then the data present at D3 will be output to Y. If D3 = 0, then Y will output a 0. The number of data inputs depends on the number of selector inputs.

For example, if there is only one selector line, S0, then there can only be two data inputs D0 and D1. When S0 equals zero, D0 is routed to the output. When S0 equals one, D1 is routed to the output. Two selector lines, S1 and S0, allow for four data inputs, D0, D1, D2, and D3.