[Coco] Using the Tandy Color Computer 3 with an RGB monitor

[CoCoList for Color Computer Enthusiasts]

On Sun, May 11, 2014 at 10:53:36AM +1000, CoCoList for Color Computer Enthusiasts wrote:
> And on the subject of RGB...
> 
> Can someone explain to me why the GIME color palette had to be
> different to the RGB?
> 
> Here in Australia, the PAL CoCo3 derives it's composite video off
> the RGB output of the GIME using a seperate daughter board
> underneath the mainboard.
> 
> But I don't understand why the GIME's built-in NTSC composite had to
> have a different palette system.
> 
> Couldn't they have derived it from the RGB internally in the GIME so
> as to keep the palette the same?
> 
> The only story I heard (if true) is that the GIME originally was
> designed for composite and RGB was added later.
> 
> Nick

This is what I meant in my recent screencast when I said that the
CoCo3's palette registers are "close" to the video output.  The bits
from the CoCo3 palette registers seems to essentially be directly
connected to the YIQ signals used to generate the color composite
video signal.  Those same bits are also forked off to the RGB video
outputs to map to the RGB color channels, with no translation for
either side of the fork.

Some contemporary systems had a chip that could map from RGB to the
appropriate colors signals for NTSC/PAL/SECAM, but I guess that Tandy
was too cheap to spring for another chip on the motherboard?

John
-- 
John W. Linville		Someday the world will need a hero, and you
linville at tuxdriver.com			might be all we have.  Be ready.