MoTeC Global Forum

A simple question - or maybe not so simple.

Can the all the devices share one CAN Bus, and by all I mean the M130, the C127 the keypad and the PDM30.

Or do I need to link the display and the ECU together via CAN2 (on the supplied "Race Loom", and put the PDM, keypad and the display on CAN1 using the "Accessories" connector.

Generally with a system like you describe, I would use only a single CAN bus for everything, including the wideband LTC for the M130.

That was how I had originally designed the vehicle harness - one CANBUS to rule them all.

A second pair of expert eyes taking a look through the workshop yesterday saw the build, asked a few questions then spoke up and said "You can't do that, it needs to be the other way". That's when my doubts started creeping in.

Thanks for your comment, David.

The only time that you really need to use seperate CAN buses in most installations is if you are connecting to two different Buses that run at different speeds, such as connecting into a OEM vehicle CAN Bus, as they normally run at 500k. I have all of that and more on a single Bus in my car, and the Bus runs at around 45% utilisation.

Did this "expert" give a justification as to why it was wired incorrectly?

Good morning Stephen - if this had happened earlier in the day I would have been pestering you on the phone.

His reasoning was that the C127 installation manual said that the terminated race loom was to be connected as specified ( DTM4M to ECU, DTM6F to all other Accessories ) and that's the way it had to be.

I am not a CAN expert by any means, and my research up to this point had tended to suggest that one CANBUS would work as I need it to, but the more I thought on it his logic sort of made sense.

I have looked through the C127 Manual, and I can see where this opinion could be formed, if taken in isolation. That section is discussing using the kit loom and the ECU to loom adapter cables that we have, in which case the ECU being connected to CAN Bus 2 and the other devices to the CAN Bus 1 connector would be correct and this would avoid having to modify the premade looms.

If you are building a custom loom, then the diagram on page 73 is the more relevant information, as it shows all of the devices on the same bus.