[Coco] 32kB carts on Coco 3
robert.gault at att.net
Tue Dec 29 20:23:19 EST 2015
RETRO Innovations wrote:
> Does anyone have a link to how it works?
> I read that it is the work of the GIME, and I assume it's the bank registers for
> task 0 and 1 (1 and 2?) that make it work, but I'm trying to understand what
> shows up on the cart port...
> Specifically, how does the upper 16kB of a 32kB cart get accessed from the cart
> port? Is the 2nd 16kB mapped to $8000-$bfff? If not, then where?
If you look at the bits for $FF90 either in the Service manual or the Spectra
Associates series, you will see:
$FF90 - initialization register 0
BIT meaning value
7 coco 1=Coco1&2 compatible
6 M/P 1=MMU enabled
5 IEN 1=chip IRQ output enabled
4 FEN 1=chip FIRQ " "
3 MC3 1=DRAM at $xFExx is constant
2 MC2 1=standard SCS
1 MC1 ROM map control
0 MC0 ROM map control
MC1 MC0 Mapping
0 x 16k Internal, 16k External
1 0 32k Internal
1 1 32k External
Based on the above, the external 32k cart should be addressed from $0000-$FFBF
or perhaps $0000-$FFEF. I'd think the former.
More information about the Coco