Re: Does anyone understand this...

[philip@labtam.labtam.oz.au (Philip Stephens)]

Gary Desrochers writes:

>I need to know what a 
>
>BIT $CFFF
>
>does.

As you may or may not know, addresses $C800-$CFFF are reserved for 2K of
ROM that any card in any slot can use.  That is to say, any card is allowed
to map 2K of ROM into that address range.

However, obviously only one card can use that address range at any given
time, so there must be a mechanism for a card to grab control of it.  The
address at $CFFF is reserved for this purpose--a card wanting control of
the $C800-$CFFF address range must read or write to that address (can't
remember the exact details).  All cards that use that address range must
listen for an access to that address and relinquish control.

Full details are in the Apple // reference manual, and I think in the Apple
//GS hardware reference.  If you want, I can look up the exact details for
you and post them tommorrow (if someone doesn't jump in and answer it for
you).

-- 
| Philip Stephens, Systems Programmer. | %%%%  %     Labtam Australia Pty Ltd |
| Address:  43 Malcolm Road, Braeside, |   % % % %     "Applied Ingenuity"    |
|           Victoria, 3195, AUSTRALIA. |  %  % %  %  We make the fastest RISC |
| Internet: philip@labtam.labtam.oz.au | %%%%% %%%%% X terminals in the world |