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SN65HVD33DR chip for RS485 half duplex operations.

Shashikiran Dayalan
Prodigy 10 points
Other Parts Discussed in Thread: SN65HVD33, SN65HVD78, SN65HVD10

I would like to know how to use SN65HVD33 chip for RS485 half duplex operations.

Should the shorting of the transmit pair and receive pair be done outside the chip or has it been done inside?

The enable pins( DE and RE) are also permanently enabled in  the circuit I reviewed...which I think is wrong and must be user controlled for RS485 half duplex operation.

please comment

Shashikiran

India

  • 0
    TI__Mastermind 21336 points

    Hi Shashikiran,

    The receiver and driver are not internally connected. This type of device is usually used on two separate networks, one network for the driver and one network for the receiver. That way if all the nodes on the network are full-duplex the master can have a private bus for sending out requests and the second bus can be used for all the returning signals. In addition, it also allows each node to both send and receive data at the same time as opposed to half-duplex which only allows a node to either send or receiver.

    More information can be found in the following application note:

    http://www.ti.com/lit/an/slla272b/slla272b.pdf

    If you plan to short the transmit pair and receive pair I would recommend looking into one of the many half-duplex devices we offer at:

    www.ti.com/rs485

    In terms of the driver and receiver enable signals, if the driver is always enabled, then it will not allow any other node to access the bus. There will always be contention since its driver will always be active.

    Please let me know if you have any other questions.

    Thanks,

    John

  • 0
    Expert 2585 points

    If you would like to use SN65HVD33  in the half duplex mode you should connext Rx and Tx outside the chip.

    RE and DE signal should be controlled from controller.

    Anyway if you like to use half duplex mode I would  recommend you look to the half-duplex transceiver as SN65HVD78 or SN65HVD10. At least this give you smaller package and simplify board design. As additional bonus you will have better price as well.

    http://www.ti.com/lsds/ti/interface/rs-485-products.page#p305nom=3.3&p1065=Half&p1690=No