[Coco] Coco3 backwards compatibility

[Gene Heskett]

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
>
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-- 
Cheers, Gene
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