M800, GEMS and 2D logger

[Stenley]

I am trying to connect a 2D stick canbus logger to an existing wiring loom in an EVO X.
The EVO X is equipped with a M800 that is sending data to a GEMS dashboard.
I connected two more wires in parallel just before the canbus wires enter the GEMS connector.
Now from here the two extra wires run (twisted) to a 2D canbus logger.

The problem is that when I connect either the 2D logger or a MICROCHIP Canbus analyzer in "listen-only" mode strange data comes in (only two strange CAN-ID's like 0xC3). When I connect either of the two devices in "normal mode" the right can-ID's are being observed, but I don't want to run in "normal mode" as it effects the system (fan starts running etc).

As there is already a direct connection between the GEMS dash and M800 ECU I would think I could run the 2D logger in "listen-only" mode as all acknowledgements should already be given by the dash.
I have tried running with or without the 100 Ohm resistor at the end of the canbus but this did not make a difference.
Does anybody know what could be wrong?

[Stephen Dean]

Hi Stenley,

I haven't used the D2, GEMS or MicroCHIP tool together, so I am unsure if there are address conflicts that may be causing your issues.

Just a a generic checklist to go over with CAN Bus errors.

The first area to check is the data rate that you have the devices set at, the EVO X M800 runs at 500k bus speed, and all of the deives that are connected to the CAN bus need to be set to the same speed. If they are not then you will get errors on the bus.

The next area to check is the base address of each device, if they are in conflict, then you will also get errors.

If these two areas are fine, with the speeds and addresses all correct, then the next step will be to connect up each device to the CAN Bus individually, and see if one of them causes the error, when this is done, you need to work out what is causing it, and then resolve the issue. We can't support the devices other than the M800 regarding this, you will need to speak to the manufacturers of the other products for support on their products.

[Stenley]

So I managed to make some progress. I checked everything mentioned including baudrates etc.
When I implemented a 100 kOhm resistor on the wiring near the 2d logger, I got a lot less errors on the canbus, but now and then the error count still went up to 128, causing an error on the ecu and the fan to go on and off.
Now I do not fully understand as I thought the dash and motec ecu were the ends of the branch needing the resistor and the parallel tap for the 2d logger didn't.
Does this mean I made an error with the wiring or the wire length? I did use a twisted pair ofcourse.
I appreciate every help.

[Stephen Dean]

Hi Stenley,

The CAN Bus should have a resistor at each end of the bus, with the devices connected to it as branches off the main "trunk" the branches should be no longer than 500mm if possible as well.

If you have a look at the M800 manual in the CAN Bus communications section, there is a diagram that shows how we recommend that the CAN Bus is laid out.