need suggestion on CANFD sample point setting with multi devices, S32K3, IMX93

[andes]

We encountered the following phenomena during use.

There are multi devices on the same CANFD bus, one controlled by IMX93, one controlled by S32K, other are controlled by MCU.

The data rate in the arbitration phase is 250K, and the sample point is 87.5%.

The data rate in the data stage is 1M, and the sample point is 75%.

When the terminal resistor is not well matched, the S32K3 will not be able to communicate, and other devices could communicate well.

Please suggest what optimization could be done to improve it; and do you have any special requirements for the setting of sampling points in CANFD?

[andes]

Hi Petr,

Thank you for the support. Customer studied the suggestions you gave and checked their settings, seems no error found in their design. The phenomenon is still there: if the terminal resistor is not well matched, the S32K3 will not be able to communicate, and other devices could communicate well.

So, the questions becomes to: if S32K has something special on the signal quality? Do we have material / data on this? 

[PetrS]

Hi Andes,

there is not much to do on S32K3 side, beside bit timing setting, you can only control drive strength for TX line, if it brings any issue with respect of EMC or something like that. S32K3 just provide the digital bit stream to be transmitted and read back stream converted from bus and processing within FlexCAN. For bus related question you should rather consult App hint document for used CAN transceiver. It discusses typical application connection and hints for each pin of it.

BR, Petr

[PetrS]

Hi andes,

CAN bus must be properly terminated to ensure that signals do not reflect back into the network, preventing signal degradation and data errors. There would be some App hint document for used CAN transceiver, which discussed typical application connection and hints for each pin of it.
In case of communication error you can check FlexCAN module error status registers to know type of error detected. Also measuring CAN bus and transceiver TX/RX signals can say more.
There can be just improper CAN bit timing configured on S32K3. BItrate and sample point should be set similarly for each nodes connected. Be sure CAN protocol clock is not running from internal FIRC, use rather FXOSC source.
Below are some interesting papers dealing with CANFD bit timing:
Recommendation for the CAN FD bit-timing
Robustness of a CAN FD Bus System – About Oscillator Tolerance and Edge Deviations
Bit Time Requirements for CAN FD
Below excel tool can be used to ease CAN bit timing calculation
https://community.nxp.com/t5/MPC5xxx-Knowledge-Base/MPC5xxx-S32Kxx-LPCxxxx-CAN-CAN-FD-bit-timing-cal...

Hope it helps
BR, Petr