De-Multiplexer

The de-multiplexer is the inverse of the multiplexer, in that it takes a single data input and n address inputs. It has 2ⁿ outputs. The address input determine which data output is going to have the same value as the data input. The other data outputs will have the value 0.

Encoder

Just opposite to decoder an encoder has many inputs but less outputs.

Below figure shows an example of 4-to-2 Encoder 

Multiplexer

A multiplexer performs the function of selecting the input on any one of 'n' input lines and feeding this input to one output line.


Assume that we have four lines, C0, C1, C2 and C3, which are to be multiplexed on a single line, Output (f). The four input lines are also known as the Data Inputs. Since there are four inputs, we will need two additional inputs to the multiplexer, known as the Select Inputs, to select which of the C inputs is to appear at the output. Call these select lines A and B.
The gate implementation of a 4-line to 1-line multiplexer is shown below: