[Coco] Artifacting (again)

[gene heskett]

On Thursday, September 02, 2010 09:25:38 am Mark McDougall did opine:

> On 2/09/2010 9:38 AM, Arthur Flexser wrote:
> > I think the explanation of the discrepancy is rather due to the fact
> > that the CoCo 1&2 had two different modes of displaying the artifact
> > colors, randomly determined after a restart or the pushing of the
> > reset button.
> 
> No, that explains the phasing of the 6847 clock, which switches the
> red/blue or orange/cyan, but doesn't change the colour sets.
> 
> I'm starting to think that red/blue is orange/cyan on different
> monitors/TV's? Can anyone concur?
> 
> Regards,

The "NTSC" signal, usually thought of as a two field interlaced model, was 
converted to a 4 field pattern when color came to the scene.  The diff is 
that fields 1 and 3 started at one color phase, and 2-4 were 180 degrees out 
so the dot crawl on a high bandwidth B&W tv was also interlaced and much 
less visible.

The coco video is not interlaced in any manner, chip circuitry to do all 
that, when the coco was new, would have tripled the chip count in the 
machine. The simple /4 from a 14.xxxxxx mhz crystal to get the color 
frequency was not preset as to divider state, so the color phase could be 
reversed at random by hitting the rest button.

-- 
Cheers, Gene
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