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SN65HVD888: Question for SN65HVD888 intermittent communication error issue

Jacky Wang(QD)
Genius 11610 points
Part Number: SN65HVD888


Hi Team,

Our customer is using SN65HVD888 in the system and will see intermittent communication error issue. The abnormal error waveform is captured as below, it looks like when error happened, the differential A-B signal amplitude will be reduced. We checked customer's schematic and PCB board and not find issues. Can you help to check what's the possible reason for this error waveform?

1. Error waveform:

2. Customer's circuit for master and slave node:

Thanks a lot!

  • +1
    TI__Guru 53575 points

    Hi Jacky,

    Thanks for sharing this issue and providing the scope shot and schematic. 

    My first thought here is that the larger A-B differential we see could be caused by multiple transceivers driving simultaneously. The combined strength of the drivers would be able to generate a larger differential across the bus termination. It appears that this jump occurs right after the system is idle for a moment (differential is zero) before the MCU drives TX. If the other node were to believe it had priority on the bus at this time, this may cause both to drive the bus here. 

    Would it be possible to capture a scope showing the 485-EN signal of both boards during such an error? If the above case is occuring, I would expect to see a moment where both EN signals are high which would cause both transceivers to be active. 
    I would also be interested to see the abnormal differential voltage in more detail. Can a similar scope shot as shown above be shared with a smaller time scale? It would be good to see individual bits to see if there's a point where the bus moves and TX is not driven. 

    Let me know if you find out anything else in the meantime. 

    Regards,
    Eric Schott

  • 0 in reply to Eric Schott1
    TI__Genius 11610 points

    Hi Eric,

    Thanks a lot for the reply and suggestions, finally we do checked and found it is related to customer software wrong EN control for one slave node. This problem has been resolved now. Thanks a lot for the help!