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SN65HVD1780: RS485 communication

sankar itraju
Prodigy 50 points
Part Number: SN65HVD1780

Tool/software:

Hi Team,

We are planning to establish an RS485 communication bus with 100+ devices connected in a daisy-chain configuration. We intend to use the SN65HVD1780 RS485 driver IC. Please help confirm whether this driver IC is suitable for our application. Here are the details of our setup:

  1. The master device is an Atmel microcontroller.

  2. The RS485 bus length is approximately 300 meters.

  3. The environment is noise-free.

  4. The communication baud rate is 19200 bps.

Additionally, please suggest the precautions we should take while designing both hardware and software.

Thank you!

  • 0
    TI__Guru 72981 points

    Hi Sankar,

    That data rate and distance should be fine and also includes the internal fail safe feature (Vth+ is negative). The device you picked also has a low UL (low leakage) which will help you support 100+ devices especially if you are using the daisy chain method (the method TI recommends for RS485 with multi nodes). 

    Is there only one master/transmitter node on the bus that won't ever change?

    Main things to keep in mind:

    • keep stubs to a minimum
    • Impedance match the RS485 traces to be the same impedance as the cable you intend to use
    • RS485 traces should all be the same length with minimal routing that goes through vias
    • If only one transmitter node, place the termination resistor on the furthest node if possible
    • Consider placing external fail safe resistors on one node just in case some noise couples on the cable when the driver is not active

    Feel free to also reach out for a schematic review of the RS485 device you choose to use. 

    -Bobby

  • 0 in reply to BOBBY
    Prodigy 50 points

    Thank you so much Bobby I will check and updates you very soon...