[Coco] Any info on a mystery 256 color GIME mode?

[Roger Taylor]

At 07:13 AM 12/3/2003 +1000, you wrote:
>I was just wondering what your opinions are on my personal quest to resolve
>the secret 256 color mode...is it real or is it fake?
>Read my web page I have created documenting all the information I have
>collected to date.
>http://www.nickm.launch.net.au/ProjectArchive/256mode.html
>Nickolas Marentes

My guess at the moment is that there's a hidden or undocumented switch in 
the GIME that enables the upper 2 palette bits, maybe enabling an intensity 
field of the usual xxrgbrgb color format.

If this secret mode is actually the same palette of 16 colors that can hold 
iirgbrgb values, then that's 4 intensities of an RGBRGB combination that 
yields one out of 64 possible colors.

Perhaps these upper 2 bits can only be active at a certain time, or by 
performing a "secret" process.

--

My big question is: is this 256-color mode a secret mode or a real mode 
that was being put into the CoCo 4 prototype?  I came across some CoCo 
write up, I think on one of the museum sites, that mentioned a CoCo 4 was 
being designed but never made it.

If the CoCo 3 guys snuck their photo into the ROM, then my guess is that 
somebody was either trying to sneak a 256-color mode in, or that there was 
actually going to be such a mode, since a 16-color mode just wouldn't cut 
it in a new CoCo model, especially when other computers at the time were 
doing 256 colors easily.

If this mode does exist in the CoCo 3, then we have 2 GIME chips to hack to 
death in order to discover it since the interviewed developers can't seem 
to recall anything useful to us.

We also have to ask ourselves, what amount of memory is required to support 
256 colors at a time.  It seems to me that each pixel would have it's own 
byte or palette indice.  That's roughly 64,000 bytes for a 320x200 
screen.  51,200 bytes for a 256x200 screen, etc.  It's easy to compute by 
multiplying the width times the height.