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SN65176B: RS485 communication error

Brian Wang0928
Genius 14040 points
Part Number: SN65176B

End-customer returned a motor driver that has found the communication error of the RS485 with SN65176. as you can see the waveform in the attached file, when /RE pin is pulled low by MCU, the V_AB differential voltage is dropping to -500mV and it triggers R pin to be low level. It could cause the communication error between motor drive and encoder side. please find the attached file for more details. very thanks. 4477.SN65176 Communication issue.pdf

  • 0
    TI__Guru 52172 points

    Hi Brian,

    Thanks for sending this over! 

    I have a couple questions to clarify:

    1. How does the other side of the RS-485 Link look like - do all the RS-485 Transceivers share the same set-up / schematic as shown in the power-point?

    2. There are a few missing component values that could be part of the issue - so if you could provide the values for R5, C315,  and C316 - I will also say those two capacitors (315,316) are not something that we recommend to put on the lines as they can load the transceiver and distort output signals. I am not sure if this is the actual issue, but knowing their values will be helpful. Also if you could get the part number for the Protection diode they have on the A/B line that will also be great. 

    3. What is the data rate that you are operating at? 

    4. Are the scope shots of two different parts - one bad and one good ? 

    Please let me know as it does look like the Receiver is reading a logic low as the customer is describing, but the passives on the line could be potentially causing issues so please let me know!

    Best,

    Parker Dodson