[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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-- 
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