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SN65HVD51 Full to half duplex conversion

Oscar Terron1
Prodigy 230 points
Other Parts Discussed in Thread: SN65HVD51, SN65HVD54, SN65HVD3088E

Dear All,

I need to use a board that is equipped with the SN65HVD51 RS845 full-duplex transceiver,  for the communication with an half duplex device, with minor changes on the board.

I may connect the SN65HVD51 output of the transmitter to his input, by the connection of the 'A' to 'Y' and the 'B' to 'Z'. In terms of software, I may program my micro controller to disable the reception while I am transmitting (eventually I need to add some time delay after the transmission end, before enabling the reception again).

The communication will work properly between my full duplex board with the SN65HVD51 and the half duplex device?

Best regards,

Oscar

  • 0
    TI__Prodigy 740 points

    Hi Oscar,

    Thanks for your post.

    Unfortunately it is not possible to use the SN65HVD51 in a half-duplex application as desired. This part has no enable/disable functionality for the driver and thus it is permanently on. If you connect driver and receiver together as needed for half-duplex, you will always have an occupied bus by this driver. This does not allow a reliable communication (In half-duplex the driver needs to be disabled to release the bus and to receive).

    So there will not be an easy way with minor changes in your layout. If you would use a full-duplex transceiver like the SN65HVD54 (which has 14 pins, but driver and receiver enable functionality) you could implement the described use case.

    Else I would recommend to replace the SN65HVD51 with a half-duplex part like the SN65HVD3088E and change your layout accordingly.

    Please let me know if I can further assist you.

    Best regards,
    Chris

  • 0 in reply to Christian Klickow
    Prodigy 230 points
    Hi Chris,

    Well, I can add some resistors to the SN65HVD51 transmitter lines, but that is not a solution.

    The problem is that i don't have a control line to control the data direction.

    I found one TI competitor that has a half-duplex driver with an inbuilt auto-direction control. I will test it and check the results.

    TI has on his range a similar device?

    Best regards,
    Oscar
  • 0 in reply to Oscar Terron1
    TI__Prodigy 740 points

    Hi Oscar,

    unfortunately we don't have a single-chip solution for data direction control and a RS-485 transceiver. You would always need at least one control lone total for DE and \RE.

    I would be interested how you would implement the solution with the SN65HVD51 and the resistors in the transmitter line. Could you please let me know how you would place the resistors to achieve a working bidirectional communication?  

    Thank you and best regards,
    Chris