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LCE
LCE
Principal II
November 14, 2025
Solved

FDCAN H7 BRS failure with Kvaser Leaf 3

  • November 14, 2025
  • 11 replies
  • 640 views

Heyho,

after some *** CAN beginner mistakes on my side, I got the FDCAN BRS 8 Mbit working.

Or so I thought. It's only working between my custom boards, as I found out after connecting a Kvaser Leaf v3.

With the Kvaser (directly connected to the board's D-sub, termination on, signals on the scope look good (enough)) and BRS on, it only works with max 2 Mbit, and only if the Kvaser's bit timing is set below 70% sampling point.

So far I played with changes to TDC, sampling point, SJW, and all bit timings (checked the Kvaser timing website).

Any ideas welcome!

Best answer by LCE

Problem solved, Kvaser replied, saying that definitely 2 terminating resistors are needed on the bus, and:

 

When using CAN FD it is extremely important that ALL nodes on the CAN bus use exactly the same settings.

That was it, I didn't know that. I thought the sampling point might be something device / interface / endpoint specific.

Luckily I made all bus parameters editable (via http PUT), so when setting the sampling point to exactly the Leaf's settings, it works.

Thanks to @mƎALLEm and to Kvaser for the quick replies! :)

 

Edit:

Interestingly, the settings must be the same not only for the BRS data phase, but also for the arbitration phase.
Without BRS it didn't really matter where each side's sampling point was.

11 replies

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LCE
LCEAuthor
Principal II
November 18, 2025

Same explained here:

Importance of the Sample Point Configuration in a CAN FD Network - KnowledgeBase - Vector Support

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