[Coco] GIME questions

[Robert Gault]

David Gacke wrote:
> One final question before I dig into this. Are GIME registers FF90 and
> FFAx readable?
> 
> I'll try and verify their contents as well, if they are.
> 
> 
> 
> Dave
> 
> 
> -----Original Message-----
> From: coco-bounces at maltedmedia.com [mailto:coco-bounces at maltedmedia.com]
> On Behalf Of Robert Gault
> Sent: Monday, August 16, 2004 1:27 PM
> To: CoCoList for Color Computer Enthusiasts
> Subject: Re: [Coco] GIME questions
> 
> David Gacke wrote:
> 
>>Hi Robert,
>>
>>Here's the setup I've got. I've got a daughterboard I made jammed into
>>the 6809 socket of my CoCo 3. Then I have a ribbon cable back to my
>>dsPIC demo board with a 30F6014 on it.
>>
>>Connected to that, I have a Microchip ICD2 pod for downloading new
> 
> code
> 
>>into the microcontroller.
>>
>>The CoCo 3 itself is a stock model with 512K of RAM.
>>
>>But from what you're saying, maybe I have a high order address line
>>hosed up or something.  I'll double check those again with the scope
> 
> to
> 
>>verify.
>>
>>Who knows. Maybe I've just got bit addr15 and addr14 shorted or
>>something goofy.
>>
>>
>>Thanks for your help.
>>
>>Dave 
>>
> 
>  ><snip>
> 
> I was about to suggest the same thing. Why don't you scan memory from 
> $0-$7FFF in both normal and 32K ROM mode and see if the ROMs echo in the
> 
> $0-$7FFF region. If they do, then both your high order bits and RAM/ROM 
> selection isn't working correctly.
> 
> It is a result similar to a 128K Coco3 when the MMUs are set to $00. 
> Some early programs needed to be rewritten when 512K boards showed up 
> because the programs ignored bit high order MMU bits.
> 
> 
The MMU registers $FFAX are readable but $FF90 is not.