I have retrofit a Wiz820io on a board that used a Wiz812MJ. I don’t have a dedicated reset line on the mother/main board. I am unable to reset the Wiz820io and it does not function. I can manually reset it using a jumper on the board but that is not possible when in actual use.
I now see the problem is that the Wiz820io has a 10k pullup on the RESETn line, and the Wiz812MJ does not. My design relies on my controller to pull the RESETn line low through a 5k resistor, so clearly the W5200 RESETn pin never sees a low level input. I have two ideas/questions:
Q1: Can you post the location of the pullup resistor on the RESETn line? I can’t trace it visually since it jumps to the other side of the board under the Magjack. I should be able to remove this and resolve the problem. NOTE: I am using Wiz820io Rev 1.0.
Q2: Is there a way to force the W5200 into a known state without using the RESETn line? I tried to send a software reset by setting bit7 of MODE register but that does not work. Can I assert/release CSn several times (or some other sequence) so that the W5200 will recognize me writing the reset bit to the MODE register?