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SN65HVD485E: RS485 issue

Anupam Nalgundwar
Prodigy 10 points
Part Number: SN65HVD485E

HI,
I am using RS-485 chip from TI part no- SN65HVD485ED . when I connect my device to single node the error rate is below 5%.
But when I connect three or more than tree nodes in parallel than the error rate is more than 15%. in our circuit we have not put, any series resistor. we kept provision of pull and pull down but not assembled. And we have put termination resistor of  120 ohm at starting and end.

Please help us out here. Are we putting wrong termination resistor or these chip is not cable of supporting multiple device.

  • 0
    TI__Guru 62920 points
    Anupam,

    The HVD485E device would be able to support many more than three nodes, and the termination you described (two 120-Ohm resistors, one at each end) is correct. Can you please probe the "D" input signals, "A" and "B" bus signals, and "R" output signals at each node so that we can try to figure out what exactly is going wrong?

    Also, at what data rate are you operating? And, are you making sure to only enable one transceiver at any given time (assuming a shared half-duplex bus is used)? In other words, the "DE" pin should be high on at most one transceiver at any given time.

    By the way, it looks like this thread addresses a similar issue:

    e2e.ti.com/.../604794

    If this is actually the exact same issue, we can consolidate the feedback into a single thread to make it easier to follow.

    Best regards,
    Max