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Original question:

SN75176BDR interface

SN75176B :SN75176BDR

youngju cho
Prodigy 40 points
Part Number: SN75176B
Other Parts Discussed in Thread: SN65HVD72, STRIKE

I implemented RS485 communication using SN75176BDR.
What I'm curious about is the effect on the SN75176BDR if the RS485- and RS485+ on the Slave side are incorrectly wired.
In fact, if I implemented it, the SN75176BDR is burned out.
Please let me know if there is any chance of burnout if I simply miswired the Slave.

I look forward to your friendly TI response. Thank you.

  • 0
    TI__Guru 62910 points

    Hello,

    This should not cause damage to the device.  Communication will not work with the incorrect wiring assignments, though.  Swapping RS485+ and RS485- would effectively invert the polarity or the bus, so a high level on "D" would result in a low output on the bus, and a high input on the bus would correspond to a low output on the R pin.

    Regards,
    Max

  • 0 in reply to Max Robertson
    Prodigy 40 points

    However, the device was already damaged by an unknown impact. I tried debugging, but I confirmed that unknown power is applied through the RS485 communication line from the slave device.
    Are you sure that such an abnormal voltage cannot be generated when the device is damaged due to incorrect connection between R pin and D pin?

  • 0 in reply to youngju cho
    TI__Mastermind 25705 points

     Youngju,

    Could you find a way to prove the damage is due to the mis-wire? Can you give the detail of the test setup, like supply, pin connection, pin status, etc? Also can you please confirm which pins were connected mistakenly, A, B, R, D?

    Regards,

    Hao 

  • 0 in reply to Hao L
    Prodigy 40 points

    The circuit of my device or slave device is designed normally without any special problems.
    If you check the device for damage, the wires connecting the device are reversed. The connection is between the A and B pins of my device and the A and B pins of the slave device. There are no other pins connected incorrectly.

  • 0 in reply to youngju cho
    TI__Mastermind 25705 points

    Youngju,

    Thanks for the schematic, which looks good to me. Several more questions: 1) what's the RS-485 device on the master side? 2) when you found the device damaged, what's the status of the system, powered up, powered down, the master sending data, etc? 3) can you repeat the failure? 4) if mis-wiring is the cause, do you know why it didn't impact the master?

    Again, in general the power doesn't flow into the bus pins. You can refer to Figure 18 (page 16) on the datasheet of SN65HVD72 for the equivalent schematic. The diode are integrated to prevent this happening.  

    www.ti.com/.../sn65hvd72.pdf

    Regards,

    Hao

  • 0 in reply to Hao L
    Prodigy 40 points

    My device is the master device. My device is a wall pad, and the slave device is an electric remote meter reading device.
    If the device is damaged, the system power is supplied, but RS485 communication is not possible. If you check at this time, the SN75176BDR chip is damaged.
    Failure repeats.
    The reason I think wrong wiring is the cause is because I haven't found any other wrong causes.
    My device is connecting 13 RS485 slave devices, and one wrong wiring gives similar impact to other devices with unknown probability.
    If SN75176BDR is used by changing AC power to DC, can AC power be released and flow to the bus line after the chipset is damaged?

  • 0 in reply to youngju cho
    TI__Mastermind 25705 points

    How far is it from the master device to the slaves? How is the grounding among the devices? Can you check if there is any ground potential difference? Other than grounding, is it possible that the bus got any over stress strike? Has any TVS diode showed any sign of being triggered?

    I'm not sure what you meant if the AC power can flow to the bus line. If the device is powered by a DC supply, would not it be the DC power flowing in? Depending on how the device is damaged, it's possible that the supply is short to the bus.

    Regards,

    Hao