I’m with a problem with W5100. The SPI comunication works ok in a develop board (WIZ812MJ) the socket open normally. But in my custom board (schematic attached), the socket not open, after send a open socket command, the S0_SR every returns “0”. I tried with socket 0, 1 and 2 and give a same result.
Perform dump of all common registers, at least some power up with 1 bits in them. If all will appear to be 0s, then you most probably have issue with clock or reset. Why do you use this circuit for reset? Use scope to see if reset signal on the RESET pin complies with the described in datasheet.