[Coco] Coco 3 Missing Mystery Color Mode

[Robert Gault]

Steve Ostrom wrote:
> This may seem like a very foolish question to those of you on the list
> who are Coco hardware experts, but I had to ask.
>
> I was reading a 1989 Coco-Link magazine from Australia this weekend and
> came across this bit of information I had never heard of before. They
> stated that the PIA outputs, which control the display modes of the
> video display chip (6847) on the Coco2, are not connected to anything on
> the Coco3. They went on to show a hardware project that could use these
> unused PIA outputs.
>
> I'm not sure that the above information is even true, but if true, could
> our missing high color video mode be a result of this "non-connection"?
> (OK, go tell me to crawl back in my hole.)
>
> -- Steve --

Steve,

I've not seen the article but doubt it implied the unused lines could be used 
for new video modes. The Coco1 and 2 have one of the PIAs connected to the 6847 
and that is not done on the Coco3. However, there is no 6847 chip on a Coco3 and 
the GIME simulates some of the 6847 functions. The only line on the GIME that is 
"unused" is the TEST line which is tied high. It's possible that the PIA with 
unused lines could be tied to the GIME TEST line but it is not likely to result 
in any new video modes.

If you study the schematics for both the Coco1 and Coco3, you will see that you 
are off on a wrong track.