understanding multiplexing

Hello all,

Just became a member on this site but I'm not new here.  I've used this site many times before to help me with wiring specs, how to wire relays and other stuff.

So time has come for me to become an advanced MECP, and I got sorta puzzled here on the part on multiplexing.  I'm trying to understand the whole concept and I think I got it figured out but still kinda fuzzy. So here's what I got out of it. Any feedback would be greatly appreciated. Please feel free to correct me if I'm wrong at all.

A typical car these days has some 5-6 miles of wire. So multiplexing is the solution to weight and cost issues, since in multiplex circuits, one wire supports multiple functions. On top of this, multiplexing gets data from point A to point B more efficiently by widening the bandwith. And whether its 10 bits or 10 megabytes the speed in which this data transfers on this multiplex "superhighway" is always the same (roughly 66% the speed of light). So is the purpose of multiplexing to increase the bits per second, widen the lanes on the freeway, or both?  And will this even be on the test? (brain nerve now swelling)

My personal take on it, and it may just be my opinion, but multiplexing and data signals are two different concepts.

Multiplexing is is a way of encoding multiple signals on one wire, usually by varying voltage (0-5vdc or 0-10vdc analog signals), by current (0-20ma or 4-20ma are commong) or by pulse widths (servo control).  In cars, generally you will only see voltage multiplexing and it's usually not 0-5vdc analog, it's usually a few precise voltages somewhere between 0 and 5vdc.  An example of this would be steering wheel buttons for radios, cruise control, air conditioning, etc.  If you push one button it will drop the voltage to 0.5vdc, another would drop it to 1.0vdc, and so on.  In the typical car scenario there are a limited number of possibilities.

Data signals are different because they follow protocols (RS232, CAN, LIN, etc).  They have baud rates and have start/stop bits and data bits as well as other parameters predefined.  A data signal can transmit much more data much quicker then a typical multiplexed system.

Chungo, so what sections of the MECP advanced textbook would you recommend to study the hardest? And should I memerize the Power, Ohm, Current, Voltage Pie Chart? Is there lots of math questions? Thanks for your reply...