topic Re: S32K311 - FlexCAN using FIRC not working in S32K

S32K311 - FlexCAN using FIRC not working

geeznxp — Fri, 03 Apr 2026 12:03:45 GMT

I'm trying to implement FlexCAN using FIRC clock mode, but not able to successfully tx and rx CAN data. However, CAN is able to tx and rx when FXOSC is configured. According to the Clock diagram, FlexCAN is using FIRC_CLK (/2) on 24Mhz resulting in 500kbps CAN bit rate. I don't understand what I'm doing wrong.

Please refer to the Clock settings below. I'm attaching code base zip as well.

Please help me run FlexCAN on FIRC.

Thanks

#s32k3

Re: S32K311 - FlexCAN using FIRC not working

Julián_AragónM — Mon, 06 Apr 2026 22:20:14 GMT

Hi @geeznxp,

I've imported and tested your project. I can see both 014h and 015h IDs being sent correctly when connecting a PCAN-USB analyzer:

However, CAN bit rate is set to 250kbps with 87.5% SP, not 500kbps:

You can calculate the bit rate values for 500kbps using the MPC5xxx/S32Kxx/LPCxxxx: CAN / CAN FD bit timing calculation tool.

Best regards,
Julián

Re: S32K311 - FlexCAN using FIRC not working

geeznxp — Tue, 07 Apr 2026 09:30:43 GMT

What hardware module are you using?

Re: S32K311 - FlexCAN using FIRC not working

geeznxp — Tue, 07 Apr 2026 09:31:38 GMT

Thanks for your response.

What hardware module are you using?

Re: S32K311 - FlexCAN using FIRC not working

geeznxp — Tue, 07 Apr 2026 13:48:44 GMT

I'm receiving BUSHEAVY when the same firmware is tested on PCAN-View resulting in no data reception.

What could be the reason to get BUSHEAVY status ?

Re: S32K311 - FlexCAN using FIRC not working

Julián_AragónM — Tue, 07 Apr 2026 21:54:31 GMT

Hi @geeznxp,

I tested your SW in the S32K31XEVB-Q100 Evaluation Board. I connected CAN Rx/Tx to PCAN-USB analyzer and tested with 250kbps.

Can you try one of the available examples from the RTD package? Or alternatively, these community examples:

As for the PCAN error message "bus heavy", that is a very broad description. Could you confirm if your bus has correct terminating resistors?

Best regards,
Julián

Re: S32K311 - FlexCAN using FIRC not working

geeznxp — Wed, 08 Apr 2026 07:27:18 GMT

Hi Julian,

Thanks for your response.

After referring to the examples you have shared, I have made another program having CAN tx and rx on interrupt with sampling point as 75% and running entirely on FIRC.

But I'm still not able to receive data on CAN. Whereas if a CAN message is sent from PCAN its response is successfully received. But messages are not getting transmitted on the specified interval.

I'm attaching the screenshots as well as zip file. Can you please take a look at it ?

Thanks

Re: S32K311 - FlexCAN using FIRC not working

Julián_AragónM — Wed, 08 Apr 2026 23:36:06 GMT

Hi @geeznxp,

I've also tested your SW with PCAN USB correctly, both with 0x240 & 0x420 IDs:

I imagine you are using a custom board, correct? I strongly suggest comparing your design with either S32K31XEVB-Q100 EVB or S32K312EVB-Q172 EVB. Specifically, the CAN interface. You can also refer to S32K3 Hardware Design Guidelines.

Also, please check the terminating resistors. I think the issue is due to bus termination.

Best regards,
Julián

Re: S32K311 - FlexCAN using FIRC not working

geeznxp — Thu, 09 Apr 2026 07:10:53 GMT

Hi @Julián_AragónM,

Thanks for your help.

Yes I'm using a custom board to test.

I was successfully able to execute CAN on the above firmware when I changed a few CAN settings attached in the screenshot.

I'm not sure what is the root cause of it, but as of now it is working with BTR 0 = 40h and BTR 1 = 2Bh Sample point 81%.

I would also compare the design with the EVB boards you have linked.

Thanks so much