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jwtuttle
Associate II
July 6, 2026
Solved

FDCAN bus acknowledge

When using the FDCAN peripheral on a STM32H743 or a STM32H753 and the message filters are setup to only accept certain messages, does the FDCAN hardware ACK a valid message that is rejected by the message filter?

Ozone
OzoneBest answer
Principal
July 7, 2026

Yes, always.

Read the CAN specification.
If a message does not get acknowledged, the sending node would go eventually into an error state, and temporarily shuts itself off the bus.
The acknowledge orininates from the CAN peripheral (Bosch IP block), as soon as it receives a valid CAN frame.

The transmission on the physical layer and the internal processing of messages are not tightly coupled.

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2 replies

mƎALLEm
mƎALLEm
ST Technical Moderator
July 6, 2026

Hello,

Not specific to STM32 but to the CAN protocol. The ACK bit is generated automatically by the CAN/FDCAN cell when at least one CAN node has received the frame correctly. By "received the frame" I mean a correct frame not necessarily passing the CAN filters.

Hope I’ve answred your question.

 

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Ozone
OzoneBest answer
Principal
July 7, 2026

Yes, always.

Read the CAN specification.
If a message does not get acknowledged, the sending node would go eventually into an error state, and temporarily shuts itself off the bus.
The acknowledge orininates from the CAN peripheral (Bosch IP block), as soon as it receives a valid CAN frame.

The transmission on the physical layer and the internal processing of messages are not tightly coupled.

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