STM32F446RE CAN Works in Loopback Mode but Not in Normal Mode

[AsmaEST]

Hello,

I configured CAN communication between two STM32F446RE boards. The code works in Loopback Mode, but not in Normal Mode.

I did not use an external CAN transceiver, as I read that direct communication is possible on the STM32F446RE.

What I have tried:

• CAN initialization is correct, and messages are transmitted successfully in Loopback Mode.
• In Normal Mode, HAL_CAN_AddTxMessage() returns HAL_OK, but no messages are received.
• Connected CAN_TX of Board 1 to CAN_RX of Board 2 and vice versa, with a shared GND.
• Enabled CAN interrupts and checked for errors using HAL_CAN_ErrorCallback(), but none appear.

[mƎALLEm · Accepted solution]

Hello,

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@AsmaEST wrote:

I did not use an external CAN transceiver.

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You can't do that in Normal mode. You need a transceiver for each CAN node.

And this is the (minimum) structure needed for this mode:

There are other methods without transceiver that I don't recommend.

But if you are connecting Tx to Rx (like an UART communication) this is not the correct HW for CAN and this will never work.

Hope that answers your question.