The holes in the range ED40 to ED7F typically duplicate documented
instructions:

- NEG at ED4C, ED54, ED5C, ED64, ED6C, ED74, ED7C
- NOP at ED77, ED7F
- RETN at ED55, ED65, ED75
- RETI at ED5D, ED6D, ED7D
- IM ? at ED4E, ED6E
- IM 0 at ED66
- IM 1 at ED76
- IM 2 at ED7E
- IN F,(C) at ED70
- OUT (C),0 at ED71

IM ? sets the interrupt mode flip-flops to an undefined state, which
seems to act like IM 0 or IM 1. These states are indistinguishable
on the CPC (!CPC chooses IM 0 to indicate an abnormal state).

IN F,(C) performs the input operation, setting the flags as normal,
but throws the input value away.
OUT (C),0 outputs zero to the port.

(Note it would output 255 if the Z80 used in the CPC were the CMOS
variant rather than the NMOS variant.)