[Coco] Hidden 256-color mode

[Boisy G. Pitre]

On Jul 26, 2005, at 3:28 PM, 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.

I wish you luck on that, Nick.  I've been trying to get Allen to ship  
a HUGE box of old Microware disks to Tim Lindner for months now.  If  
you find the secret that gets him to the post office, please let me  
know.

Boisy