Re: Apple II+'s 16K RAM Card

["Michael J. Mahon" <mjmahon@aol.com>]

Bryan Parkoff wrote:
>     Apple II+'s RAM card contains 16K which it looks like from $C000 through 
> $FFFF, but 12K is already taken from $D000 through $FFFF.  It is very 
> possible to modify RAM card by adding two RAM chips which it gives a full 
> 16K from $C000 to $CFFF.(excluding $C000-$C7FF)
>     You may know that I have Saturn RAM card with 256K, but 256K is divided 
> into 16 banks that shows only 12K out of 16KB which it gives 192K out of 
> 256K.  It seems to be confused when "Understanding Apple II+" manual says to 
> implement bank-switching from $0000 to $BFFF and from $D000 to $FFFF while 
> text/lo-res and hi-res are not affected.  It means that you can reroute your 
> applications to RAM card rather than access memory from motherboard while 
> text/lo-res and hi-res still access memory from motherboard.
>     It does not make sense.  Can you please have an explanation what it 
> means?

Bryan, you have been associated with the Apple II for some
time, yet you apparently do not do even minimal reaearch into
things before asking here...

The 16K RAM card _is_ a full 16K.  The lower 4KB, which
you seem to want to map from $C000 to $CFFF, is actually
mapped as an alternate bank from $D000 to $DFFF, which
allows it to be used while still maintaining access to
Apple II memory-mapped I/O.

The details of enabling for reading/writing/or both,
in both the primary and secondary bank, are detailed
in numerous places.

The Apple //e and later (64KB+) machines implement this
same mapping scheme for the $Dxxx pages.

-michael

New Applesoft BASIC interface for NadaNet networking!
Home page:  http://members.aol.com/MJMahon/