A multiplexer (MUX) is a device that can receive multiple input signals and synthesize a single output signal in a recoverable manner for each input signal. The simple function of selecting and routing logic function transmitting data from several sources on one common transmission line.

A multiplexer can be thought of an electronic switch as shown in fig.

A multiplexer has

1. Data inputs: The data inputs are used to input the binary logic levels or data, to be switched to the output of multiplexer. A multiplexer has several data inputs, but only one data input can be switched to the output at any one time.

2. Select inputs: The select inputs are the address input for the multiplexer. The address on the select inputs determines which data input is switched to the output. Each data input requires its own address, which is unique binary combination that is specified on select inputs

3. Output: The multiplexer is programmed through the select inputs to establish a connection between output and addressed data input.

Application of Multiplexer

Multiplexers are versatile circuit that are used in application such as

a. Data selection: The data from only one device is selected to be transmitted on the common channel at a given time but multiplexer can address any of the device output when necessary. This application is referred to as data selection, is commonly used to reduce the cost of separate transmission facilities.

b. Cascaded operation: Multiplexers can be cascaded together to increase the number of data inputs that can be transferred to a single output. Cascading is a technique where several MUX chips are wired to work together.

c. Binary word multiplexing: Binary word multiplexing is an application where all the bits of binary words are switched in parallel or simultaneously through a MUX circuit. Binary words are typically a 4 bit nibble or a 8 bit byte.

d. Time division multiplexing: Time division multiplexing is a complex form of data selection that is very important in digital transmission systems. It is used extensively in public and private telephone networks for transmission of many voice data, video images on common transmission line. In time division multiplexing applications, many devices share a single transmission line. Each device sharing the transmission line is assigned a time slot for transferring its data. The output multiplexed data is organized into frame which contains one slot of data from each device.