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THVD1450: Single-end transmission for RS485...

Peter Tseng
Mastermind 6200 points
Part Number: THVD1450

Dear Sirs,

Is it possible to use RS485 with single end mode?

i.e. only connect A or B with both RS485 IC?

If yes, how to deal with the unused pin? pull high or pull low

  • 0
    TI__Guru 53575 points

    Hi Peter,

    Though I can see how a working implementation of what you've described is possible, a design like this would lose much of the features that make RS-485 desirable. If a single-wire, single-ended solution is what you're looking for, modifying an interface protocol such as LIN, RS232, or IO-link may offer better solutions. These standards typically offer higher voltage and slower slew-rate drivers which help with the drawbacks of not having a differential data line for common-mode noise rejection. If you would like help choosing which of these may work best for your system, please share some more information regarding your use-case and requirements and I'll try to outline some benefits each may provide. 

    To answer your question, in an RS-485 application where one of the bus lines is held at a constant voltage, it would be best to keep in between the high-driven voltage and low-driven voltage. This will likely be around Vcc/2. [Edit] Note this should be done carefully so that the driver does not draw/sink too much current when trying to drive the unused pin.

    Please let me know what other questions you have regarding how to implement you transceiver layout. 

    Regards,
    Eric