This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

SN65HVD1473: RS485 Communication Issue

Part Number: SN65HVD1473
Other Parts Discussed in Thread: SN75176B,

Hi,

I'm using two RS485 transceivers to communicate between two controller cards.

Below are the two different part no's

SN75176B

SN65HVD1473 

SN75176B part works under 5 volt supply and SN65HVD1473 works under 3.3 volt supply.

I'm trying to send/receive data between two controller card using these two Transceivers.I have probed single ended signal and taken screen shoots. 

The prob 4 shows the data transmitted from the controller 2 and and Probe 2 shows the data received at controller 1.

I have noticed that the transmitted data from the Controller 2 is not exactly received at controller 1(controller 1 is in Receive mode)

But Data sent from controller 1 is received properly at controller 2(Controller 1 is in Transmission Mode) .For clear details please refer the attached document.

Please can any one suggest what could be the reason for this issue.

RSS485 COMM.pptx

Regards

Ashok

  • Hi Ashok,

    Thanks for providing the scope shot. That looks a little strange. Can you please tell us what the other two probes are showing? And, have you tried probing the differential signals? That might give us a better understanding what could be going wrong in this system.

    Max
  • Hi Ashok,

    Is the bus between the devices failsafe biased? If both drivers are disabled, the bus could float and produce indeterminate values when read from either side. To keep the receiver outputs at a logic high while idling, a differential voltage should be applied to the terminated bus. This will ensure that when neither device is driving the bus, the receiver output will not change.

    The newer RS-485 models can maintain steady outputs without failsafe biasing, which is why the indeterminate doesn't show up on the SN65HVD1473 side.

    Find more in this app note:

    http://www.ti.com/lit/an/slyt514/slyt514.pdf 

    Let me know if this makes sense.

    Regards,

    Eric

  • Hi Ashok,

    Just checking back in - were you able to resolve this issue? Is there any other feedback we can provide?

    Thanks,
    Max