Any technical gurus know what i need to read Can-bus

[clever dicky]

Hi I believe Can bus is a fairly standardised system, from make to model.

But i would like to know of a simple method to read the can, and specifically know that the lights are on. Possibly other info.

I know there are proprietry can readers for various ICE systems, but i would like to know if MB does maintain can info accross the range and whether there is info available, non generic, that better explains the decoding needed, ie specific can intergration to read can codes.

I can find info on the can pins, voltages, pulse widths etc. But not on code tables or devices to latch on specific data words.
Any ideas?

Hope someone here knows even what I'm on about

 

[Alex Crow]

For sure it ought to be easy, there ought to be a bus plug in that could capture a log and allow chronological interpretation or real time interraction to enable hybrid functions.

However, it is not easy, and there isn't, other than stuff like this CANCapture: Advanced CAN Diagnostic and Analyzer Software

For sure it will come, the can communication chips in modules must be pretty cheap to produce, but the real problem is going to be coping with all the data and working with the vehicles complex comms protocols etc.

There is a free demo download on the cancapture site, and lots of info, well worth a look.

 

[schneckster]

CAN Bus is a standardised comms protocol and is ideal in high noise environments such as cars. But there are a couple of versions and this requires a little knowledge of the end application or what the manufacturer has used.

CAN messages comprise of, amongst other things, message identifiers and data. The data is sometimes not even used as CAN devices can be programmed to see a message identifier differently to other devices. An analogy:

Go into two Chinese takeaways and order a number 15. You'll probably get two different dishes as a result. They both know what they have to do with "number 15", but it won't be the same as the other. On a car, two seperate devices would see the message and do two entirely different things.

And herein lies the problem. Message identifiers are the part of the CAN system that tends to be proprietary. In other words, unless Mercedes release a full list of what each message identifier means, all you will see if CAN messages bouncing back and forth. Adapting the Chinese takeaway analogy, message 15 on a Merc may be to put the headlights on, whereas on a BMW it may mean put the windscreen wipers on. Without the manufacturer releasing that information, we would never know by looking at the CAN bus.

As Alex Crow points out, reading the CAN bus is easy. It's the interpretation of it that isn't unless you have help from Mercedes.

Schneckster