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ISO3086: Full-Duplex Feature not working properly

beto_rousseaux
Prodigy 30 points
Part Number: ISO3086
Other Parts Discussed in Thread: ISO1452, ISO1412, ISO1432

Hello everyone!

I designed a board that uses RS485 communication protocol and I have an issue when trying to make it work as full-duplex.

Every time I try to send data without disabling receiver, I receive a start bit and nothing else. Then, my uC understand that a new byte has arrived so it tries to process it.

The workaround I implemented is to turn receiver off when transmitting (it's like a "manual" half-duplex), but that's not what I am aiming to since I chose this IC because of its full-duplex feature. I measured the signals with an oscilloscope and I realized that everytime I sent a message, there's a small signal on the receiver side of the IC (RX and RX' are not connected to anything).

My question is: is it the way it works? Should I turn the receiver off everytime I send a message?

Thanks!

  • 0
    TI__Expert 6195 points
    Hi Beto,
    Sorry you are having trouble with the ISO3086. This behavior is unexpected. Would you be able to provide your schematic and any pictures of the oscilloscope waveforms your were seeing so I can help you debug this?
    Best regards,
    Dan
  • 0 in reply to Dan Kisling
    Prodigy 30 points

    Hello Dan,

    Thank you for your answer!

    I've  solved the problem. The IC is working as it should. The problem was that when I was testing Tx, I forgot to place a termination resistor in Rx and Rxn pins (these were not connected to anything), so the noise was enough to be detected as a logical "1" and therefore I was reading a start bit with the IC and hence, with the uC.

    Thank you again for your time!

  • 0 in reply to beto_rousseaux
    TI__Expert 6195 points
    Hi Beto,

    Thanks for following up and posting the solution! Please feel free to post in the E2E forums if you need any additional help.

    Also please note that there is a new family of full duplex isolated RS-485 transceivers - The ISO14x2 family (ISO1412, ISO1432, and ISO1452). It has a higher isolation rating, increased EMC protection, a wider supply range, stronger CMTI and better isolation immunity and robustness.

    Have a great day!
    Dan