There are differences between the NMOS and CMOS implementations of the Z80. And an FPGA is neither NMOS or CMOS [1]. This is an interesting post describing the

There are differences between the NMOS and CMOS implementations of the Z80. And an FPGA is neither NMOS or CMOS [1]. This is an interesting post describing the hoops one has to jump through to replicate an NMOS chip in an FPGA [2]. [1] https://sinclair.wiki.zxnet.co.uk/wiki/Z80#Differences_between_NMOS_and_CMOS_Z80s https://sinclair.wiki.zxnet.co.uk/wiki/Z80#Differences_betwe... [2] https://baltazarstudios.com/z80-ground/ https://baltazarstudios.com/z80-ground/