Multiplexer to De-Multiplexer.

This is a question I always wanted to ask in my Digital Electronics; course at my grad college. I never asked this question though, knowing that it sounded very stupid. Anyways I knew that my lecturer wouldn't have had appreciated a student curious to this insane, blow up devices, level.

So what is a multiplexer?
A simple device, which routes any one of the N inputs to its sole Output line. The selection being done by the signal you feed it on, very aptly called, the Selector Lines.

To make the dump readers understand what it is like, it is like a junction on the road where all except one roads are two-way. Now traffic from which road enters the one-way is determined by the traffic signal, the selector lines.

For the dumber, its like this. You have a house and you need hot water, cold water or no water. So you have three water lines, one carrying hot water, one carrying cold water and one carrying no water. So if you want to get hot or cold or no water (the N =3 inputs lines) in your kitchen tap (the sole output line) you use a switch/level/valve (the selector).

For the dumbest, there's is nothing like Multiplexer, its all my imagination.

What is a demultiplexer?
The reverse, route the sole input to one of the many output lines, using the selector lines to select which output.

Well actually the multiplexer is on a chip, and one chip usually has 3-4 multiplexer depending on how many inputs you have. So you cannot take one multiplexer and tell others "Hey do you see this? This is a multiplexer!"

Coming back to the question, a rather dump one after having given the above examples!!

If we can give signals at input and choose which one to route on the output line, using the selection lines; why can't we give the input on the sole output line, use the selector lines to select which output line and route the signal to the selected line. A decoder!!"

Caution: The term input output lines are relative and to make the statement less convoluted, the input/output lines are used as seen from a multiplexer.

BTW I don't know why the lines are called lines? I guess the trend started because:

• It was easier to print straight lines in the books rather than curves.
• Since, people who taught and people who were taught saw the straight lines, started calling it lines (synonymous with straight lines!!)