For the people who haven't noticed: Yes, Z80 has 64kB I/O space (16 bit).
For "IN A,(n)" and "OUT (n),A" A is used as the upper 8 bit.
For "IN r,(C)", "OUT (C),r" and OTI/OTD/OTIR/OTDR, actually BC is used as
the I/O address!
The reason it's not used much (although I think I remember something about
Spectrum using it), is because of obvious reasons.
IN A,(n)/OUT (n),A are close to useless to access 16 bit I/O devices, but
can ofcourse be used on 8 bit devices. The same counts for
OTI/OTD/OTIR/OTDR, since is constantly being decremented, so is the upper 8
bit of the I/O address!
IN r,(C)/OUT (C),r are the only I/O instructions to reliably work with 16
bit I/O devices.
Z380 supports 32 bit I/O addresses in the same manner. For IN A,(n)/OUT
(n),A the upper 16 bit are always zero (handy), and for all others the
entire 32 bit BC is used.
To enable a sane use of the 'extra' I/O space, I/O devices should just
ignore the the 2nd 8 bit (high byte of the low word) of the I/O address.
Patriek
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