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SN65LBC184: communication error

Part Number: SN65LBC184
Other Parts Discussed in Thread: SN65HVD3085E,

Hello Experts,

My customer is facing a communication error. Customer is connecting between SN65LBC184 and SN65HVD3085E. He mentioned that communication error occurred if termination resisters mounted. Would you please check the schematic and the waveform? If you find something, please let me know how to resolve this error. Also the external failsafe circuit is required at SN65LBC184 A/B-pins? It seems that this phenomenon occurred after SN65LBC184 DE goes High to Low transition. (I think SN65LVC184 A/B-pins went Hi-Z.)

https://tidrive.itg.ti.com/a/UI4-C9yOPhdCjj4R/99142c11-7699-42ad-b85d-1909a00a2abb?l

Best Regards,
Fujiwara

  • Fujiwara-san,

    The schematic looks good to me. However the waveforms are puzzling. I'm not sure why the bus voltage toggled as the D is high. Can you check the HVD3085E's status to make sure it was not driving the bus? Another way to check is to disconnect the HVD3085E while leaving the termination and pull up/down on and compare the waveforms.

    Regards,

    Hao

  • Hello Hao-san,

    Sorry for late reply. Customer tried changing the device from SN65LBC184 to SN65HVD3085E. Would you please confirm the attached test results and please give your comments?
    [Question]
    1. Is this the workaround?
    2. Please give your comment for customer measurement result.

    https://tidrive.itg.ti.com/a/CmZSl4ZmUoUYZlKN/58baa5fe-9aee-4571-ad9b-06dd2401fa39?l

    Best Regards,
    Fujiwara

  • Fujiwara-san,

    It might be a workaround however I suggest we do a few more experiments. BTW, is it possible to plot node 4, 7 with the differential bus voltage (TRD+/node1 - TRD-)? It looks like the communication switches sides before the bus is settled. Is it possible to add some delay between 4 and 7 to let the bus voltage have time to be pulled together by the termination? Then we can see if the SN65LBC184 still has the issue in transition and if the SN65HVD3085E fixes it. Thanks,

    Hao