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SN65HVD77: SN65HVD77DR pin swapping and length

J.P.
Intellectual 300 points
Part Number: SN65HVD77
Other Parts Discussed in Thread: AM26LV31E

Good afternoon,

i have a couple of questions regarding this part and RS485 in general.

1) I was wondering if the P/N can be swapped on these parts? Ie Z would go to P and Y would go to P. 

2) If I am allowed to swap Z/Y, does that mean that A/B must also swap?

3) do the A/B lines need to have the same length as the Y/Z lines?

Thank you for your time

  • 0
    TI__Mastermind 25705 points
    J.P.

    Unfortunately the polarity of Z/Y cannot be swapped. There is no active high/low pin on this device. TI has a quad RS485 driver AM26LV31E, which has this feature. If you were able to swap Z/Y, you would have to swap connection to the receiver input A/B as well. The receiver always takes differential voltage A-B. Please let us know if you have more questions.

    Regards,
    Hao
  • 0 in reply to Hao L
    Intellectual 300 points
    Thank you for your response. Do you know if the A/B lines and Y/Z lines must be similar in length?

    Also, I think I am missing something. I am not sure what benefit am26lv31e would provide?

    thank you!
  • 0 in reply to J.P.
    TI__Mastermind 25705 points
    J.P.
    Yes, it's also recommended to use twisted pair for better common mode noise immunity.
    AM26LV31E can swap the polarity of Y/Z by G/G_bar pin.
    Regards,
    Hao