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Original question:

SN65HVD251: CAN bus termination

SN65HVD251: Abnormal waveform discussion

Lin_Charles
Expert 4260 points

Part Number: SN65HVD251

Hi team,

My customer is using SN65HVD251 to replace PCA82C250T as a receiver, and they find that our device cannot communicate on the bus while PCA82C250T is good. I have let them get below waveform, I saw that the last bit is abnormal, could you please help share mem what may cause this phenomenon and how to solve this issue? Thanks. 

  • 0
    TI__Guru 74302 points

    Charles,

    This looks to be the ACK bit, which is a dominant bit that all nodes send at one time to acknowledge that the frame was received correctly. Because all nodes are dominant at the same time, there is a slight rise in voltage.

    When you say that our device will not work while the PCA device is good, what exactly do you mean?

    Regards,

  • 0 in reply to Eric Hackett
    TI__Expert 4260 points

    Hi Eric,

    Thank you for your response here. I have compared the datasheet of PCA82C250T and  SN65HVD251, these two devices may not p2p. Below is the waveform of how PCA82C250T behave when RS is high, the NXP device will pull RDX to low while SN65HVD251's receiver remains active. Customer needs to ignore these data, this may cause some data error for their MCU.This is their old platform, they do not want to update software, do you have some p2p solution to replace PCA82C250T? Thanks. 

  • 0 in reply to Lin_Charles
    TI__Guru 74302 points

    Charles,

    I can't see the waveforms, but I understand the problem. Pin 8 on the SN65HVD251 puts the device into a silent mode rather than standby mode, which is what the customer needs. I would recommend the TCAN1042 then. Pin-to-pin compatible except pin 5 is a no connect, because the Vref isn't needed to help with the recessive level stability on the TCAN1042. 

    Let me know if the customer can use this device.

    Regards,