[Coco] VDG weirdness

[Phill Harvey-Smith]

On 12/10/2015 19:21, Zippster wrote:
> Nice job Phill.  The output looks really good.
>
> Love the true black background on the inverted alphanumerics.
>
> So this is doing Y, øA, øB to 15KHz RGB?

Yeah takes øA, øB and CHB, and converts to a 4 bit digital output then 
takes Y amplifies it and converts to pixel on / off. At the suggestion 
of some of the Atom people I force CSS to 0 going into the 6847 and then 
used the CSS from the 6821 into the CPLD to change the colour sets 
there. This is because the voltages out of the 6847 as slightly 
different depending on CSS, doing it this way means that the 6847 always 
thinks it's CSS 0.

Output is then converted to TTL RGB and fed via a SCART to a TV.

Cheers.

Phill.

-- 
Phill Harvey-Smith, Programmer, Hardware hacker, and general eccentric !

"You can twist perceptions, but reality won't budge" -- Rush.