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Re: II specs? Help!
In article <D24AIo.43y@hkuxb.hku.hk>, William <h9104374@hkuxa.hku.hk> wrote:
> John Lundgren (jlundgre@news.kn.PacBell.COM) wrote:
Just a couple of corrections:
> Oh, each slot is allocated with 2K ROM addresses, $Cx00-CxFF for slot x.
That is only 256 bytes. Each slot has a 256 byte page allocated for
it ($C100-$C1FF for slot 1, etc.). Each slot also has 16 bytes
available for I/O, in $C0n0-$C0nF, where n is the slot number plus 8.
The space from $C800-$CFFF can be shared between all slots by a
somewhat messy bank switching mechanism (access $CFFF to disable the
expansion ROM on all slots, then access anything in $Cn00-$CnFF to
enable the expansion ROM for slot n).
> Besides, in the area $04FF-$07FF & $2000-$3FFF some addresses are
> assigned to the slots (what a mess!)
Not $2000-$3FFF, just $0400-$07FF. The last 8 bytes from every 128 in
this range ($0478-$047F, $04F8-$04FF, etc.) are reserved for use by
the corresponding slots ($0479 is for slot 1, $47A is for slot 2,
etc.) The first of each of the 8 bytes is reserved for use by the
system software.
--
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand