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THVD1406: Testing RS485 With Autodirection Control

Jason Heller
Prodigy 10 points

Part Number: THVD1406

Hello,

I have a circuit with the THVD1406 that is outputting RS485 using the autodirection control feature. I want to test the RS485 bus using a laptop. I have tried multiple RS485-to-USB adapters, but each adapter's native autodirection control conflicts with the THVD1406's autodirection control. I have been able to test my circuit using a microcontroller and a transceiver with DE/RE control to sync with the THVD1406's autodirection control, but I was wondering if there are any reccomendations of a simpler solution that wouldn't require an external circuit to be built for testing.

Thank you. 

  • 0
    Guru 325520 points

    In theory, the autodirection circuits of multiple drivers should not interfere with each other.

    What exactly goes wrong? What is the bus signal in that case? (Tell the oscilloscope to compute A − B.)

  • 0
    TI__Guru* 81381 points

    HI Jason,

    As Clemens mentioned, the auto direction feature basically puts the device into high-Z mode so it shouldn't interfere with another RS485 device that's driving at the same time but that's only when it's actually active. There's a set delay for when it actually kicks in and controlling the DE/RE pins don't really force it into auto-direction mode. 

    Do you have a schematic we can review?

    Do you have an o-scope where you can probe in D input, R output, and A-B math function?

    -Bobby

  • 0 in reply to Clemens Ladisch
    Prodigy 10 points

    Thank you for the quick response. Went back and tested it again and it ended up being a bad solder joint on my THVD1406. When reworked it worked with my USB adapter. Thank you!