FDCAN Not Transmitting or Receiving on STM32G0B1CCT6

[AKG123]

I am working on FDCAN communication using an STM32G0B1CCT6 microcontroller. I am trying to perform a simple Tx/Rx loopback test (and later communication with external tools like Vehicle Spy), but I am facing the following problem:

• FDCAN is not transmitting or receiving any message.

• I have configured the peripheral in Normal mode with the following settings:

  • Clock: 64 MHz

  • Bitrate: 1 Mbps

  • Prescaler: 16, TimeSeg1: 13, TimeSeg2: 2, SJW: 1

  • Frame Format: Classic CAN

  • Auto-Retransmission: Enabled

• I also added a filter (Filter 0) to accept all standard IDs into RX FIFO 0, but still no data is received.

• FDCAN init and message send/receive functions return HAL_OK, but no actual communication happens on the bus.

I’ve verified the transceiver wiring (ISO1044), and I'm testing using Vehicle Spy and ValueCAN4. I’ve also tried internal loopback, but still no response.

[mƎALLEm]

Hello,

There are confusing information in your post.

At the beginning you said you are trying to use loopback mode and after you said you have configured the peripheral in Normal mode.

---

@AKG123 wrote:

I am trying to perform a simple Tx/Rx loopback test 

• FDCAN is not transmitting or receiving any message.

• I have configured the peripheral in Normal mode with the following settings

---

Could you please clarify? what is the mode are you using? and which one you succeeded to perform?

 

[AKG123]

Hello,

Thank you for the response. To clarify, I have tried both Loopback and Normal mode for FDCAN on my STM32G0B1CCT6, but unfortunately, neither mode is working.

• Loopback Mode: I set the FDCAN in internal loopback mode, expecting the device to send and receive its own message. However, no data is being transmitted or received.

• Normal Mode: I also tried normal mode with the correct clock settings, prescaler, and bitrate, but again, no communication happens.

I have verified the transceiver wiring and am using a ISO1044 transceiver, and I am testing with ValueCAN4. But still, there is no TX/RX communication happening.

Can you please share any relevant STM32CubeMX FDCAN settings or suggest what could be missing from my configuration?

[mƎALLEm]

Ok, as the Loopback mode is not working it's certainly a configuration issue in your example. So if the loopback mode is not working the Normal mode will not work.

So at this stage forget about the Normal mode and focus on the External Loopback mode. No need for a transceiver in this mode.

So my question here what part is not working: the transmit or the receive? do you have a logic analyzer or oscilloscope to probe the CAN_Tx pin? so at least to check if the transmit is good.

What ID format are you using: Standard or Extended?

 

[mƎALLEm]

+

As you are using standard ID format, you have set the filter number to 0:

 hfdcan2.Init.StdFiltersNbr = 0;

In that case even you succeed with Tx, you will never succeed the receive.

So need at least to set that value > 0.

[AKG123]

Thank you very much for your suggestion.

I had initially set hfdcan1.Init.StdFiltersNbr = 0, as you mentioned. After updating it to at least 1 and properly configuring  now I am able to receive the message in External loopback mode — so yes, reception is now working.

However, transmission is still not successful.

• I checked the CAN Tx pin with a logic analyzer, and during transmit, there is no activity.

• I also checked voltage on CANH and CANL lines with respect to GND — both show ~2.5V, which is correct in idle state?

• I have attached:

  • My STM32CubeMX configuration screenshots

  • The code used

  • A screenshot from Vehicle Spy, which shows error during transmit

• I am using Standard ID (11-bit) and ISO1044 transceiver, with proper 120Ω termination.

So now I request support to understand why the Tx is failing. Any further suggestions would be really helpful.

Thank you again!

[mƎALLEm]

Hello,

I used your project with a little modification, I can see the frame on Tx pin as well as on Rx.

I used two NUCLEO-G0B1RE boards connected with two transceivers. The same example uploaded to the two boards.

This is what I can see with a CAN analyzer: Blue: Tx, Purple: Rx.

I'm also seeing the message received, which are sent by the other board:

So, either there is something transmitted on Tx but there is an issue with your logic analyzer configuration or you have something on your hardware. So check all your connections, check the GPIO pins used etc..

PS in Normal mode we recommend to use an external crystal instead of using HSI or any internal RC source.

I've attached your project with the modification.

Hope that helps.