[Coco] Coco3 backwards compatibility

[Gene Heskett]

On Wednesday 25 October 2006 08:30, jdaggett at gate.net wrote:
>Actually the pointer to the secondary vectors are hard coded into ROM and
> not in the GIME or the SAM Chip. In fact for the SAM chip, any address
> that is from $FFE0 to $FFFF will read from the ROM. I would imagine that
> the same would be true of the GIME chip in this case.
>
>The interesting thing is that the GIME chip can have the 256 byte page
> from $FE00 to $FEFF as either RAM or ROM.
>
>
Thanks for the correction, James.  My memory gets hazy when its not 
refreshed in such details from time to time.  I think they call that 
oldtimers. :)

>james
>
>On 24 Oct 2006 at 23:49, Gene Heskett wrote:
>> On Tuesday 24 October 2006 23:32, William Astle wrote:
>> >Robert Gault wrote:
>> >> The game was made to run on a Coco3 by limiting the data transfer to
>> >> an upper value of $FEED; protecting the secondary interrupt vectors.
>> >
>> >You know, I think they chose that precise location for the secondary
>> >vector table because the hex value is such a nice one to remember.
>> > I've always been struck by that. Of course, it just works out that
>> > way if you start at the top of the reserved page.
>> >
>> >Given what I know about programmer types, however, I'd almost wager it
>> >was intentional. And if it wasn't, they probably went around telling
>> >everyone it was...
>>
>> I believe it was intentional, but dictated by the fact that the last
>> few upper bytes of memory are ram regardless of the mapping of the rest
>> of the space above $7FFF.  This is hard coded into the gime, and the
>> rest of the coco and coco2 sam chips.  I've seen references to that,
>> but cannot now quote where I read them.
>>
>> >--
>> >William Astle
>> >finger lost at l-w.ca for further information
>> >
>> >Geek Code V3.12: GCS/M/S d- s+:+ !a C++ UL++++$ P++ L+++ !E W++ !N
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>> > y?
>>
>> --
>> Cheers, Gene
>> "There are four boxes to be used in defense of liberty:
>>  soap, ballot, jury, and ammo. Please use in that order."
>> -Ed Howdershelt (Author)
>> Yahoo.com and AOL/TW attorneys please note, additions to the above
>> message by Gene Heskett are:
>> Copyright 2006 by Maurice Eugene Heskett, all rights reserved.
>>
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>>
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-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Yahoo.com and AOL/TW attorneys please note, additions to the above
message by Gene Heskett are:
Copyright 2006 by Maurice Eugene Heskett, all rights reserved.