Multiplexing means transmitting a large number of information units over a smaller number of channels or lines. A digital multiplexer is a combinational ckt that selects binary information from one of many input lines and directs it to a single output line. The selection of a particular input line is controlled by a set of a selection lines. There are 2n input lines and n selection lines whose bit combinations determine which input is selected.
A in decoders, multiplexer ICs may have an enable input to control the operation of the unit. When the enable input is in a given binary state, the outputs are disabled, and when it is in the other state (the enable state), the ckt functions as a normal multiplexer. The enable input can be used to expand two or more multiplexer ICs to a digital multiplexer with a larger number of inputs.
