A multiplexer (also called a data selector) is a logic block that steers selected input data to its output. This logic function has multiple data inputs from which to choose, but only one of the inputs will appera on the output. Control signals called selct lines are used to determined which data input will be routed to the output.
For added flexibility, this chip has both a normal data output and an inverted data output, as well as a strobe or enable control input. A more detail description of the 74LS151 IC is available in the manufacturer's data book.
A demultiplexer is also called a data distributor
since it has several possible destinations for the input data to be sent
to. the single line that will receive tha data is controlled by the specific
code applied to the demultiplexer. the large arrows for inputs and outputs
in Figure 3 represent on or more lines.
The 74LS138 is an example of MSI demultiplexer chip.
It is a 1 line to 8 lines Demultiplexer. One bit of inputdata may be sent
to any one of eight possible output destinations. Data that is input to
one of the G2 enables will not inverted by the DMUX chip. The other two
enable pins may be utilized as enable controls. A more detail description
of the 74LS138 is available in the manufacturer's data book.
Figure 5 is a security monitoring system that is
to be implemented in the laboratory experiment. The system is to monitor
the open/closed status of 8 access doors in an industrial plant which are
door 0 to door 7. The status of each door is displayed on the LEDs that
are mounted on a remote monitoring panel at the security guard's station.