STM32 FDCAN node sees nothing on bus when CAN-to-USB adapter removed

[aqua_dev]

Board & Setup:

• STM32H563RGT6 running FDCAN2 in Normal mode (HAL_FDCAN_Init, Mode=FDCAN_MODE_NORMAL)

• SN65HVD230 transceiver in silent mode (Rs pin connected to 3.3V) (120 Ω intergrated) wired with a single 120 Ω terminator at the far end

• No other pull-up/down or termination changes when the USB–CAN dongle is unplugged

• Filters configured (Reading the data from the BMS of a custom battery):

  • FIFO0 → IDs 0x1E0 (BMS_STATE), 0x1E2 (PACK_MINMAX), 0x1E3 (PACK_AVG)

  • FIFO1 → ID 0x1E1 (PACK_VALUES)

Symptom:

• With the USB–CAN adapter or another node on the bus, everything works: the real BMS sends all four messages, our STM32 ACKs them, and they appear in Cangaroo.

• As soon as the USB–CAN dongle is unplugged (or if our transceiver is switched to any other mode -> Slope control or High speed (no slope control)), no messages are observed on the bus—even though the BMS should still be broadcasting at 1 Hz (it constantly spits out data at a 1 Hz rate) and our STM32 is in Normal mode.

What I need:

1. Keep the SN65HVD230 in Normal (ACK-capable) mode—tie its RS pin LOW (or drive it low in GPIO init).

2. Still “ignore” any frames I transmit (because I’m not sending any), so that I only see the BMS frames.

How do I ensure my SN65HVD230 is always in normal, ACK-capable mode (so the BMS sees at least one ACK and keeps talking), while my STM32 itself continues to filter out any of its own (non-existent) messages so I only capture IDs 0x1E0–0x1E3?

***My STM32CubeIDE "main.c" is given in attachments.

[Karl Yamashita]

Your seg2 is almost the same as seg1. So your sampling point is almost in the middle. You want to sample close to 87% give or take

If the FDCAN clock is 50MHz, then try these values

[aqua_dev]

I changed to the typedef union which is practical, but does not eliminate the problem of the communication. Also I changed to HSE clock which is 12 MHz in my case so I now have different parameters for the same bitrate (250 kbits/s), but it does not seem to be the solution.

[mƎALLEm]

Please attach your ioc file.

[aqua_dev]

I'm using my 12 MHz HSE with these parameters.

[aqua_dev]

Here's my .ioc file as of now.

[Karl Yamashita]

If you are using HSE for the FDCAN, do you actually have an external oscillator? If so, what frequency?

[Karl Yamashita]

Assuming you have an external clock at 12MHz, try the attached IOC changed to use 66MHz and use the values below. I have values for 12MHz as well

	Baud 250000 bit/s
FDCAN clock freq(kHz)	seg1	seg2	prescaler
12000	39	8	1
66000	219	44	1