Re: Apple II II+ Mountain Comp Expansion Chassis

[Eric Smith <eric-no-spam-for-me@brouhaha.com>]

"Bill Garber" <willy46pa@comcast.net> writes:
> Judging from the placement of the cable on the interface card,
> that would be replacing one of the 74LS138's which would expand
> the slot capability. As you may not be aware the Apple II is capable
> of defining the eight slots as 0-7 and then again as 8-15. If the box
> contains firmware to feed the Apple II, there is no reason why all
> 8 of the slots in the box can't be defined from slot 7. If I'm wrong
> please correct me, but I believe I am reading all these manuals in
> the correct way. The slots can be used through locations C000-
> C7FF and C800-CFFF.

If you're talking about mapping the Cn00 space for the extra slots in
the range C800-CFFF, that could cause problems.  Apple defined the
C800-CFFF space to be shared between all the cards (except slot 0).
The protocol is that any access to Cn00 of a particular card (i.e., n in the
range of 1 to 7) will enable that card to use the C800-CFFF space.  An
access to CFFF is supposed to disable the C800-CFFF space on all cards.
Not all cards use the C800-CFFF space, but most of the fancier cards do.

Also, the firmware on normal cards "expects" to be in the Cn00 space
where n is in the range of 1 to 7.  It's likely that many cards wouldn't
work properly for n in the range of 8 to F.

The low-memory slot globals (hidden in the unused part of the page 1 text
screen between 0400 and 07FF) also only have room for eight globals for
each of seven cards.  (The other eight globals are used by DOS.)

If I were building an expansion chassis, I'd design it such that under
software control each card in the expansion chassis could be mapped
under software control to replace one (selectable) card/slot in the
computer.  I'd provide both user utility software to control the mapping,
as well as subroutines and technical documentation to allow it to be
done from user-written or third-party software.

But I have no idea what Mountain Hardware/Mountain Computer actually
did.  I always wanted on of those but couldn't justify the price.