[Coco] Hidden 256-color mode

[Robert Gault]

Nickolas Marentes wrote:
><snip>
> Nick replied:
> What I was referring to was an RGB mapped 1 byte per pixel mode... 
> something possibly along the lines of RRRGGGBB. The y component in 
> yyyyrgb I think refers to intensity, which is normally associated with a 
> composite signal I think. (RGB with 16 levels of intensity). This actual 
> mapping could be wrong because my "contact" couldn't remember exactly. 
> As for semigraphics mode, yes, it could be even that...but how to turn 
> it on is the million dollar question.
> 
 ><snip>

Well rrrgggbb would not be good. Whatever levels to be used should be 
evenly divisible by three. yyyyrgb certainly would have y=luminance but 
that in no way implies that the output is a composite signal.

Based on the actual Coco3, the most likely mapping might be pppppppp 
where p determines the palette value in a 256 palette map. The output 
could be either or both composite and rgb dependent solely on the DAC 
inside the GIME chip. I'd think that would be the simplest way to 
retrofit backwards from 256 colors to 64.