Re: What Apple II cards used the $c800 ROM address space

["Laine Houghton" <laine@intergate.com>]

"Robert L. Doerr" <rdoerr@bizserve.com> wrote in message
f33567e7.0405200601.6ce54ec9@posting.google.com">news:f33567e7.0405200601.6ce54ec9@posting.google.com...
> Hello,
>
> I appreciate the explainations.  All this time I have used the Apple
> and I never knew that many of the cards used bank switching in that
> way.  These newsgroups are great!  I learned something new.
>
> From what I understand (in the example of the SSC) is that the actual
> resources of the card like the Serial UART would be memory mapped to
> the address range for the slot it is in.  What I am still unclear about
> is that once that is accessed would that enable it's ROM starting at
> address $c800 or would a portion of it also be mapped or reside in the
> memory reserved for the slot?  Until I can see the schematics or find
> those specs I guess it could be either way.  I am looking forward to
> finding out for sure.
>
> Now, if some of the emulator experts care to jump in perhaps they can
> suggest some ways the additional ROM of the SuperSerial card could be
> added to an emulator so it would then be compatible with Apple programs
> that require it.
>
> Thanks again for the help.
>
> Best Regards,
>
> Robert

This is generalized as certain slots have certain restrictions.
Each slot in the apple //e has the exclusive use of 256 bytes of rom
address, 8 bytes of ram and 16 I/O lines. Cards that wish to use the 2K
expansion rom space $C800 - $CFFF must follow the rules. They must include
circuitry such that a when the address lines for $CFFF becomes active they
unlatch their expansion rom from the address space. Most cards use a simple
nand gate arrangement so when $CFxx is active they unlatch and thus they
loose the last 255 bytes of expansion rom. When a card whishes to use its
expansion rom it does a read or write to $CFFF. This causes any card using
expansion rom to unlatch from the address space (including its own). When
the card next address its own slot its expansion rom will be available from
$C800-$CFFE. Or with the simple nand gate from $C800- $CEFF.