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SN65HVD31: SN65HVD31 config to haft duplex 2 wires communication

Paul Tran
Intellectual 280 points
Part Number: SN65HVD31

hi TI expert 

we made design with full duplex RS485 with SN65HVD31
but now, our application need communication with 2 wires haftduplex external slave device 

Could you please help to share config of 4pin out of SN65HVD31 for connection with 2 pin of an external slave device

with this setup, when host send anydata that alway loopback to host, that is the issue now. 

  • 0
    TI__Guru 62920 points

    Hi Paul,

    Unfortunately it isn't possible to use SN65HVD31 as a half-duplex transceiver.  The reason is that there is no way to disable the driver circuit - it will always send a voltage onto the bus, and this will prevent any other nodes from being able to use the bus to send data.  (In half-duplex networks, it is important to make sure only one driver is active at a given time.)

    An exception to this would be if the communication only needs to occur in one direction (i.e., from the host to the device).  In that case you could either leave A and B disconnected or leave R disconnected in order to prevent the echo-back function.  (Or, in many cases this can be ignored via firmware.)

    If you were using a full-duplex transceiver with "DE" and "/RE" enable controls, it would be possible to operate in a half-duplex fashion by connecting "Y" to "A" and "Z" to "B."

    Max