Nxp S32k312 CAN bit timing parameters Issue

[Anitha7]

Hi, @lukaszadrapa 

We are using the FlexCAN0 module for CAN communication. To configure the baud rate, we are using bit timing parameters.

Configuration Details

Device	S32K3xx - CAN FD	fpe_clk [MHz]	40
Transceiver	TJA1046	bitrate [kbps]	500
propTXRX [ns]	150	bitrate FD [kbps]	2000
bus length [m]	40	samp. point [%]	90

Our requirement is to achieve a tolerance of ≤ 0.4% for the following parameters:

1. Nominal Bitrate: 500 kbps

• Prescaler: 4

• PropSeg: 7

• PhaseSeg1: 10

• PhaseSeg2: 2

• RJW: 2

2. Data Bitrate (for BRS): 2000 kbps

• Prescaler: 1

• PropSeg: 7

• PhaseSeg1: 6

• PhaseSeg2: 6

• RJW: 6

Issue Description

The CAN communication works correctly without Bit Rate Switching (BRS). However, when BRS is enabled, we encounter TX errors.

We are using an FXOSC input clock of 40 MHz for the CAN module.

Could you please help us fine-tune the bit timing parameters to achieve a tolerance ≤ 0.4% with BRS enabled, using the 40 MHz FXOSC input clock?

[PetrS · Accepted solution]

Hi, 

you can try below tool for CAN bit timing parameter calculation;
https://community.nxp.com/t5/MPC5xxx-Knowledge-Base/MPC5xxx-S32Kxx-LPCxxxx-CAN-CAN-FD-bit-timing-cal...

Also see some hints below...
- If possible, select same prescalers for both nominal and data phases.
- If have TDC enabled, try to disable it as it is not needed for this rates.
- Be sure all node use same CAN protocol (non-ISO vs ISO CANFD).
- Have bus properly terminated.

BR, Petr