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TCAN4550: sample point issue

Part Number: TCAN4550

Tool/software:

I have a question about the TCAN4550 sample point issue.

I set the bit rate to 500k/2M and the sample points to 70%/75%.

Is this setting correct?

For testing, I connected the TCAN4550 board with Vector CANAnalyzer equipment.

The CANAnalyzer was also configured with the same settings.

When sending data from TCAN4550 with BRS enabled, the CANAnalyzer receives it well without error frames.

However, when sending data from CANAnalyzer with BRS enabled, the TCAN4550 board doesn't receive it.

When BRS is disabled, the TCAN4550 board receives the data well.

So, I lowered the sample point in the CANAnalyzer settings to 60%, and then the TCAN4550 board successfully received the data even with BRS enabled. Is there something wrong with my sample point settings?

  • Generally this issue is due to different bit rate configurations between the two nodes that results in a different sample point within the bit period.  But if I understand you correctly, your issues come when the settings are the same, but you don't have issues when the settings are different.

    When you say that you configured the same settings into the CANAnalyzer, does this just let you set the sample point and bit rate, or do you get to configure how many time quanta (tq) are used per bit period just as you do with the TCAN4550?

    The actual Bit Rate Switch occurs at the Sample Point in the BRS bit of the CAN FD message.  If both devices do not have the same settings, one device will switch to the faster Data rate before the other device which can result in a sampling error. 

    I calculate a Nominal Sample Point of 80% and a Data Sample Point of 75% based on the number of tq that you have allocated per bit period.  If your nominal sample point is actually 80% in the TCAN4550, but 70% or 60% in the CANAnalyzer, then this may result in a the devices switching to faster bit rate at different times and cause the errors.

    Regards,

    Jonathan