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Thread: At Relaxkit 4500 Ethernet TX wires interchanged

  1. #1
    Intermediate Intermediate Ing99 is on a distinguished road
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    At Relaxkit 4500 Ethernet TX wires interchanged

    Hi Infineon,

    at Relaxkit 4500 Rev1.2 the TX connections from phy (IC200) to RJ45 (X200) are interchanged, TXP is connected to TD- and TXM to TD+. Please is there any reason for or is this an error?

    Best Regards
    Wolfgang

  2. #2

    Infineon Employee
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    jferreira will become famous soon enough
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    Hi,

    I would advise to follow Design Checklist at https://www.microchip.com/wwwproducts/en/KSZ8081.

    Regards,
    Jesus
    The views expressed here are my personal opinions, have not been reviewed or authorized by Infineon and do not necessarily represent the views of Infineon.

  3. #3
    Intermediate Intermediate Ing99 is on a distinguished road
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    Hi Jesus,

    thanks, the checklist says:
    "MDI Connections: Pin 1 of the RJ45 is TX+ and should trace through the magnetics to TXP (pin 7) of the KSZ8081RNB. Pin 2 of the RJ45 is TX- and should trace through the magnetics to TXM (pin 6) of the KSZ8081RNB."

    So there is no reason to interchange the tx connections.
    But TX+ connected to TXM and TX- to TXP only results in a phase change by 180 degr, at clock frequency of 125 MHz (100 MBit/s) and a wavelength of about 2 meters in the cable it's like a cable length difference of 1 meter between tx and rx line. This doesn't affect the clock recovery in the phy, it will compensate this phase difference, so this 'wrong' connection also runs.

    Best Regards
    Wolfgang

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