Notes:
* The opcode ED70 reads the port indicated by the register C without keeping the result but modifies the register F
* The opcode ED71 is used in many PSG players/drivers, as it's very useful for the PSG access, which sits behind the PPI. But beware, on a CMOS Z80 this opcode behaves differently. It corresponds to the instruction OUT (C),255 on a CMOS Z80#FF instead
* The opcode EDFF is used by Winape (and other emulators) to break into the debugger (a 'break opcode') [https://www.cpcwiki.eu/forum/emulators/shakerland-portal/msg244578/ Source]