CAN Outputs - weird outputs

[Ian]

Hi Everyone,
My 1st post, good to finally join you!

I've been using my time in lockdown to bring my e.v. project out of hibernation. The last thing I got working was reverse engineering the BMW Mini Speedometer (Regrets, I've had a few..).
Now I want to send some data to the Speedometer (via the microcontroller I'm using to drive it, if required).

I have 3 active CAN data points (according to Web interface). However, when I scope out the CAN outputs they look like this:

i.e. a 7.5us pulse roughly every 50us, with lots of decay time on the down-slope.

I have buzzed out the CAN-TX pin (JP1-3) to the CAN Transceiver and checked for shorts to other pins on JP1 and JP2 (there are none).
I have also checked for shorts between CANH and CANL and other pins on JP5 and there are none. It doesn't look like the problem is on the bus side of the transceiver, as the high and low side are both showing the same problem.

Does anyone have any ideas as to what this signal looks like or where it is being picked up from? Btw I have tested this with the CAN Bus completely disconnected from anything else on the bus.

I am running with H/W version 2 and firmware 4.85.

Thanks in advance,
Ian

[Ian]

Aaah - 120 Ohm termination resistor missing - signals were reflecting straight back into the CAN-Rx line, I guess it thought there was a collision on the bus and did an immediate retry, repeated ad infinitum..

[mdrobnak]

Welcome to CAN reverse engineering. You've learned your first lesson. What are you using to capture the data stream?

-Matt

[Hank]

Aaah - 120 Ohm termination resistor missing - signals were reflecting straight back into the CAN-Rx line, I guess it thought there was a collision on the bus and did an immediate retry, repeated ad infinitum..

So...on termination, I'm using a terminated can hat on a Raspberry pi, going straight into the pins for CanH & CanL on the Tesla motor harness, and I'm not seeing anything. Is the inverter board terminated, or will I need to account for that in my design?