This post came from QnA of WIZnet website
as I have not received a real answer on my question regarding the brownout problem (which manifested as link up/down toggling from W5300) I may put up these questions again, in the hope to get an answer from you which addresses the problem.
(A) How do I correctly sense the link status of an W5300 chip (as used on the Wiz200WEB module)?
Your very answer was to use one port pin of the ATmega128, use internal pullup and connect to the link status LED of W5300 (as WizNet forgot the PHY status registers inside W5300).
(B) If I get a toggling link up/down status, and no link, how can I get the W5300 working correctly without doing a full power cycle (and hoping that next time it will work)?
© How can I find out if the W5300 is really working as expected, and that it is not caught in some strange behaviour like described above? I use a really long reset sequence hardware wise (2 seconds after power up waiting, 1ms /RST low, 20ms delay before first access to get PLL running stable).
Would be nice to hear answers this time.