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SN65HVD888: Multi node - multi master configuration.

Shinu.V.Mathew
Expert 7465 points
Part Number: SN65HVD888

Hi Team,

One of our customer is using SN65HVD888 and having following queries, in the application where it is used for more than 200 nodes with any node can be master at a time,

  1. Can we have all nodes to be with 888 device?
  2. Where should the failsafe resistors to be connected?
  3. Because of external failsafe resistors, is there any limitation on maximum number of devices or data rate or throughput?
  4. Inputs/ reference for differential termination resistor scheme for 888 device with failsafe resistors.

Can you please help with your valuable inputs.

Regards, Shinu Mathew. 

 

  • 0
    TI__Guru 62910 points
    Hi Shinu,

    Yes, it is OK to have all nodes use the HVD888 device. The only requirement would be that the bus contains failsafe resistors so that there is a way for each node to detect a "default" polarity. Generally it is best to include the failsafe resistors only at a single node, typically one where termination is placed (although this is not required). We recommend against placing them at every node, though, since the parallel combination of all the failsafe resistors may overload the RS-485 drivers.

    Because the failsafe terminations will sink some current (similar to a receiver circuit), populating them does place some limitations on the number of devices that can be placed on a network. For a detailed description of these concerns, please reference the following blog post:

    e2e.ti.com/.../how-much-loading-can-an-auto-polarity-rs-485-bus-support

    I hope this helps, and please let us know what further questions you have.

    Max