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repeater problems

Enzo Ternavasio
Expert 1065 points
Other Parts Discussed in Thread: ISO3082, ISO3088

I have buit a data rate indipendent repeater as suggested by TI design.

With baud rate of 500k, 32 units load and 240m cable, i place repeater after 120m but it doesn't work.

It works only with short distances. If i omit to place  the repeater, and connect the 2 cables together, the line works sussesfully.

Wave shapes seems to be correct, as expected. Line termination resistence is 120ohm at both ends.

I have even tryed the circuit without optoisolation but with same results.

Thaks for any advice.

Enzo Ternavasio

  • 0
    TI__Mastermind 20820 points
    Hi Enzo,

    What type of application is this...RS-485?

    Can you please provide me the TI design number you are referencing so that I can best address your question? Also a block diagram of what is working vs what is not working (with pin configurations, i.e. is the driver/receiver enabled) will be helpful.
  • 0 in reply to Michael Peffers
    Expert 1065 points
    Hy Michael,

    my repeater circuit comes from this:
    www.ti.com/.../tida-00333;tisearch=Search-EN-Everything
    but i have changed some component.
    My purpose is to transmit RS485 data at 500k or 250k speed at distance of 500m or more.
    Now i can if i do not insert any repeater. If it was possible to upload a file i should send the circuit.

    Enzo
  • 0 in reply to Enzo Ternavasio
    TI__Guru 62920 points

    Hi Enzo,

    Could you try operating the link at a lower rate?  The ISO3082 device used in the reference design you mentioned is only rated for operation up to 200 kbps, so you may simply be trying to operate too quickly for the device.  Updating to a faster device like ISO3088 may be an option as well.

    If the speed is not an issue, then it would be interesting to see the waveforms at the input and output to the repeater to verify that everything is working properly.  Also, does inserting the repeater in the link cause issues regardless of the cable length, or do you only have problems at very long distances?  That may better help direct our suggestions for debugging.

    By the way, it is possible to attach files using the e2e forum.  You just need to click the "use rich formatting" link next to the text entry box.  That will open a more fully-featured text editor that allow for attachments or for inserting media in-line with your message.

    Regards,
    Max

  • 0 in reply to Miguel Robertson
    Expert 1065 points

    Hy Max,

    i do not use ISO3082 but ADuM1301, that can go to very high speed, so this should not be the problem. I have even tested without optocoupler. with same ground.

    The problem persists even at 250K bits/sec.  If i plug a cable of 120m, comunication with units works not more far than  60m about.

    Wave shapes seem to be correct. I  should say that is a cable problem if all  didn't work at 480m without terminator.

    I have not found "use rich formatting".

    Regards Enzo