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SN65HVD11: Termination and Works mode

Yoav Benita
Prodigy 30 points

Part Number: SN65HVD11

Hi,

Im designing new board with SN65HVD11DR.
In system will be one master board with several slave boards using RS485 channel for communication as described below.
image.png

 

In that architecture, shall i add termiation on the lines?
Shall i pull down the unused RO/DI pins?

Thanks

 

  • 0
    TI__Mastermind 21512 points

    Hi Yoav,

    Thanks for reaching out!

    I am catching up on questions, but I will get a response to you tomorrow. In the meantime, here is our RS-485 FAQ: 

     [FAQ] RS-485 / RS-422 Transceiver Resources  

    -Ethan

  • 0 in reply to Ethan Sempsrott
    TI__Mastermind 21512 points

    Hi Yoav,

    What is the approximate length of your cabling? Typically termination is recommended since RS-485 systems can be quite lengthy. 

    If the driver or receiver are not needed, you can simply configure the enable pins for each. 

    R pins can be left floating if unused. Note that tying down the driver input while the driver is enabled (DE=VCC) will cause bus contention. 

    What made you select the SN65HVD11? I highly recommend looking into our newer THVD14xx line of devices. These have improved ESD, driver strength, fault protection at a more competitive cost. 

    Best,

    Ethan

  • 0 in reply to Ethan Sempsrott
    Prodigy 30 points

    Hi Ethan,

    Thank you for your help.

    I chose the SN65HVD11 because of legacy reasons (we use that part on other boards). The master board is an old board, and I can’t re-layout it now. If I use your recommendation, it won’t be a problem that my master is SN65HVD11 and the slaves are THVD14xx, right?

    My total cable length is about 5 m (1.2 m for each slave).

  • +1 in reply to Yoav Benita
    TI__Mastermind 21512 points

    Hi Yoav,

    Understood, that makes sense. Just note that several of the THVD14xx devices are pin-to-pin compatible with the SN65HVD11 so they can simply be re-soldered on. 

    Either way, there will be no issues with using SN65HVD11 and THVD14xx devices together since they are all compliant to the RS-485 standard.

    Due to the number of nodes and cable length, I would recommend termination.

    Let us know if you have any other questions!

    -Ethan