STM32H7 FDCAN FD_MODE pin

[Siwastaja]

A quick and possibly stupid question regarding STM32H750.

What the heck are the alternative function pins:
FDCAN1_RXFD_MODE
FDCAN1_TXFD_MODE
FDCAN2_RXFD_MODE
FDCAN2_TXFD_MODE

Skimming through the FDCAN description in the reference manual, or using text search for "FD_MODE" reveal absolutely nothing. Reference manual lists all inputs and outputs of the FDCAN module, including internal-to-chip signals; no hit.

What is this thing and where's the documentation for it?

[mikerj]

Debug pins apparently:
https://community.st.com/s/question/0D50X00009XkgJx/stm32h743-what-is-the-purpose-of-pins-fdcanntxfdrxfd

Sounds like they wanted to remove them from the documentation to avoid questions, but never actually did it.
https://community.st.com/s/question/0D50X0000C5Uo6iSQC/rxfdmode-and-txfdmode-pins-what-are-they-for

[Sal Ammoniac]

This is typical of ST documentation. Lots of stuff that's absolutely necessary to implement peripheral drivers is missing, yet lots of extraneous nonsense like these CAN-FD mode pins is left in when it should have been deleted.

The ST documentation for CAN-FD in the STM32H7 reference manuals is almost a word-for-word copy of the Bosch documentation from here: https://www.bosch-semiconductors.com/media/ip_modules/pdf_2/m_can/mcan_users_manual_v330.pdf

[Siwastaja]

LOL, typical ST. No other manufacturer have any problem marking production test pins or debug pins as "TEST", "DBG", or something similar, and adding a footnote what they are.

Thanks.