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Original question:

SN65HVD31: SN65HVD31 config to haft duplex 2 wires communication

SN65HVD71:How to configure a RS485 Full-duplex transceiver as Half-duplex?

ilker TUNA
Prodigy 10 points

Part Number: SN65HVD71
Other Parts Discussed in Thread: SN65HVD72, SN65HVD70

Tool/software:

Hi,

I have designed a Full Duplex system using the SN65HVD71 transceiver. I would also like to use it in Half Duplex mode. Could you please advise me on the necessary steps to achieve this?

Additionally, I would appreciate guidance on the proper wiring configuration and whether there are any errors in my current setup.

I would be grateful for your assistance.

Best regards,

  • 0
    Guru 321540 points

    What is the purpose of R57 and R61? Termination resistors would be much larger, and must be present only at the two ends of the bus. In a unidirectional connections, only the one at the receiver is needed.

    In an integrated half-duplex transceiver (e.g., SN65HVD72), the driver and receiver are connected together. Just do this externally. But note that half-duplex communication requires the DE signal, so you cannot use the SN65HVD71 for this; you would have to use the SN65HVD70 instead.

  • 0
    TI__Guru* 79031 points

    Hi Ilker,

    Clemens comments are correct. In Full duplex mode, usually the driver(Y/Z) doesn't have the termination resistor but the receiver (A/B) would. The termination resistor should match the cable's impedance which for RS422 is normally 100 ohms though it can differ.

    For half duplex, you would connect the driver and receiver circuits to each other. 

    What exactly is your goal though? Are you planning to switch from half to full duplex in an actual application? Or you just want the flexibility to do so if needed?

    -Bobby