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Original question:

Talking to a rs 232 device with a 485 converter..

TRS3221E: RS232 and RS485 over the same two wires

Cosmin P
Intellectual 1620 points
Part Number: TRS3221E
Other Parts Discussed in Thread: SN65HVD21

Hello,

Is there a solution to use the same two wires for combining both 232 and 485 communication?

Thank you

  • 0
    TI__Guru 62910 points

    Hi Cosmin,

    It is generally possible to connect an RS-232 transceiver to the same connector pins as an RS-485 transceiver as long as you have the ability on each device to disable its respective driver output (so that multiple active drivers don't contend with one another).  An example of this is shown here:

    http://www.ti.com/tool/TIDA-00540

    Some things to be aware of are:

     - An RS-232 transceiver's "RIN" input generally has a 5-kOhm input resistance that cannot be disabled.  This can introduce some additional loading when placed on an RS-485 line.

     - Most RS-485 transceivers do not support the +/- 25-V tolerance required of RS-232 inputs.  This may not be a concern for a given application, since the vast majority of modern RS-232 drivers output a lower voltage range.  If it is a concern, though, a higher-voltage-capable transceiver like SN65HVD21 could be used.

    Regards,
    Max