Under what condition(s) is PHYCFGR-LNK set to 'Link Up'?

I’ve always assumed it means that a physical network connection is present, but searching the manual today made me realize that I don’t really know that for sure. Does anyone know for certain under what conditions this bit is set and reset?

What exactly have you made thinking this way? In my opinion it must get set when carrier signal is detected.

I was going to answer a question about a W5x00 Ethernet library that was posted at https://github.com/arduino-libraries/Ethernet/issues/111 but realized I didn’t have a definitive answer.

Your answer makes sense, but I’m hoping someone from Wiznet can confirm that’s how it works.

LNK bit of PHYCFGR operates same the link pin of W5500.
It is driven low whenever the PHY detects a valid link. We don’t know about valid link or any carrier signal because it operates internal to the PHY.