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How-to-guides - Data bus 101 (multiplexing)


Understanding data bus (multiplexing) systems and what they do


Data Bus


Also known as:

  • Logic signal.

  • Data line.

  • Multiplexing.

  • Or just bus.

This increasingly popular way to transmit electrical information thru a single wire is being used more now than ever by most automotive manufactures. Knowing how it works and plays, will expand your installation knowledge to new horizons!



Data bus





Data bus

Part 2



Data bus?


The data bus system allows one wire to send many different signals of electrical information, allowing the manufacturer to accomplish several objectives:


1. Reduce costs, as less wire is used in manufacturing of the vehicle.


With non data bus systems, vehicles are equipped with large gauge wire to send a large amount of current necessary to power a specific device.

Since most work is processed at the vehicles processor, many wire gauges are reduced to more than hale the size.


This intern enables the vehicle manufacture to reduce the cost of wire.

Most of this wire is made of cooper, do the math!


2. .Another advantage for the vehicle manufacture is that with a data bus or (multiplexing) system, it allows the manufacturer or even the owner of the vehicle to make processor changes without changing mechanical parts.



This has two advantages:


1. Vehicle manufactures are always making improvements on there vehicle. By using the multiplexing system they can "flash"  the software to the vehicles possessor, instead of having to physically change a mechanical part.


Lets take the door lock system for example.

Many vehicles have the ability to lock the doors when the vehicle is:

  • In any gear.

  • At a specific speed.


The vehicle manufacture may determine at a specific time that it is safer to have the vehicles doors lock at 10 mph, as opposed to last years model that locked at 15 mph.


2. Not only can the vehicle manufacture change this feature, but the dealer may also have access to the same modification features.


This allows the consumer to change a specific features and allow the dealer to add another service to there inventory, as most dealer may have a small fee for this service.




Getting started


Understanding a data bus signal is not as complicated as it appears.


As we discuss the basics of data bus technology you will probably have one of those   " wow, that makes sense" moments!


Now let's get to the nitty gritty.





Is it really a bus?


The best way to describe the data bus is to imagine a group of twenty people,

each with a specific task, about to board a bus.


Each person is "informed ".... when you reach your destination, perform a specific task".


As they enter the bus, the bus drives to it's destination. As each person leaves the bus, they perform the task, such as, unlocking door, roll windows up, turn cruise control on etc.






Where to now?


Now, the way manufactures perform this function is by sending multiple resistance values through one wire, as opposed to sending a positive or negative voltage to each device for direct control.


So, for example, if you want to unlock the vehicles doors, the wire must see a 10ohm resistance value through the wire.


This value is then sent from the vehicles door unlock switch to the vehicles BCM, or body control module.


The BCM is simply a microprocessor that determines what value means what and then performs the task requested, depending on the value of the resistance sent to the wire.







Continue to:

Data bus Part-2








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