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I'm working on a custom board with Texas Instruments DP83822 PHY and 100BASE-FX SFP transceiver. This is connected to a media converter via mmF fiber. The link led on the media converter never comes on. My specific question is: How does the media converter know when to turn on the its Link LED?

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How does the media converter know when to turn on the its Link LED?

When it sees the Tx signal from the other side of the link on its Rx. The signal must be at the correct frequency and strength for the specific ethernet standard (100Base-FX at 1300 nm in this case).

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  • Some media converters reflect each side's link status across the ports - so, the link only comes on when carrier detection or auto negotation are successful on both sides.
    – Zac67
    Feb 20 at 21:57

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