[Coco] Re: Hidden 256-color mode

[Robert Gault]

Nickolas Marentes wrote:

> Roger Taylor wrote:
> 
>>
>> Still, it seems that 1 byte per pixel would be required which would 
>> throw the RGB monitor into another video mode even if the colors don't 
>> appear correctly.
>>
>> I suspect that the mode invoked by holding down F2 while hitting RESET 
>> has something to do with the undocumented/hidden 256-color mode.  I 
>> see no useful purpose for this blue shade video.  Maybe a missing 
>> color component is mixed in somehow to give a new color range.  Who 
>> knows?  Think about it... they put in the 3 Mugateers picture and made 
>> IT visible by holding down CTRL-ALT-RESET, so it seems logical that 
>> the same method of hiding something was also used to help hide the 
>> 256-color mode.
>>
>>
> Nick replies:
> 
> I'm afraid it goes far beyond a simple "set of special key sequences" 
> for entry. If it was this easy, the mode would have been discovered ages 
> ago via the many dissassemblies of the ROM. This mode is, according to 
> my contact, a matter of accessing a certain location at a certain 
> refresh time during a specific interrupt event. Supposedly, some 
> register/s change during this stage to reveal the secret/hidden register 
> required. A very short "window of opportunity" you could call it.
> 
> 256 colors is possible without the traditional 1 byte per pixel mapping. 
> If you look at my research page, my contact says " It uses a yyyyyrgb 
> format, 5 bits of intensity, 3 bits of color". This may suggest that the 
> mode may only be available under the composite video out.
> 
> I think the next stage is deciphering Al's prototype.
> 
> Nickolas Marentes
> 
> 
> 
Nick,

Isn't yyyyyrgb 1 byte per pixel? If not, is it 5 pixels on or off with 
the same 8 colors?

Any chance the the "256mode" is a new semigraphics rather than PMODE 
type mode?