[Coco] 32K carts?

Joe joef6809 at gmail.com
Mon Oct 22 13:21:36 EDT 2007

It seems to work like this.
When the gime is set to 16K Internal /16K External the internal rom runs 
from $8000 to $C000 and the External rom runs from $C001 to Whatever. We all 
know that. When you switch to 32K External it gets wierd.
$C001 to Whatever is mapped to the first 16K of the ROM and $8000 to $C000 
maps to the last 16K of the ROM. This makes sense as any code running from 
rom say at $C??? would need to turn on 32K External mode, but when that 
happens if it was a liner map the code that was executing would "jump up" 
Hope I've explained this so others can understand.
When I get home I'll hack up a test version of VCC and see exactly what 
Arkanoid is doing. IE what GIME registers its trying to hit.

----- Original Message ----- 
From: "Roger Taylor" <operator at coco3.com>
To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
Sent: Monday, October 22, 2007 11:35 AM
Subject: Re: [Coco] 32K carts?

> At 09:52 AM 10/22/2007, you wrote:
>>Hi guys,
>>Is there anything special about a 32K cart?
>>I'm trying to work out why I can't get Arkanoid or Rampage to run out of
>>EPROM on my cart board. I assumed the top 16KB would get mapped into $C000
>>and the ROM bootstrap code then enables the full 32KB of external ROM 
>>But it would appear to me that Arkanoid at least doesn't do this.
>>What I think is happening atm is that when I enable the 32KB jumper on my
>>cart, the internal and external ROMs both drive when the CPU is accessing
>>memory from $8000-$BFFF and it's not a pretty sight... :(
>>So I'm wondering how 32KB carts actually function?!?
> That's something I never learned, but it seems that the internal CoCo 3 
> ROM area from 32768 to 49151 is there no matter what, and a 32k pak might 
> have to switch in 16K at a time starting at 49152/$C000, no?
> Hopefully you can add a jumper or two on your boards to fix any problems 
> like this.
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