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STM32F446RE CAN Works in Loopback Mode but Not in Normal Mode

AsmaEST
Associate

‎2025-03-25 2:59 PM - last edited on ‎2025-03-25 3:15 PM by

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.

 

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mƎALLEm
ST Employee

‎2025-03-25 3:13 PM - edited ‎2025-03-26 12:57 AM

Hello,

@AsmaEST wrote:

I did not use an external CAN transceiver.

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:

CAN.png

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.

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