Its Ethernet controller is supported by [[SymbOS]] and by [https://github.com/salafek/KCNet-software-for-Net4CPC KCNet utilities] for CP/M.
The Ethernet controller uses 4 I/O ports:
*#FD20: MR - Common Register MR
*#FD21: IDM_ARH - Upper 8 bits Offset Address Register
*#FD22: IDM_ARL - Lower 8 bits Offset Address Register
*#FD23: IDM_DR - 8 Bits Data Register
[[Media:Ethernet W5100s ds v125e.pdf|WIZnet W5100S datasheet]]