[Coco] VDG weirdness

[John W. Linville]

NTSC artifacts are an important consideration, for sure.  FWIW, what
I had in mind would be to put a certain CoCo game in a traditional
arcade cabinet (with 15kHz RGB video).  In that case, whether or not
the NTSC artifacts matter becomes game dependent... :-)

John

On Mon, Oct 19, 2015 at 05:53:48PM -0500, Zippster wrote:
> This is very similar to a board I was developing when Brendan approached me 
> with his FPGA based project, which I stopped development on in favor of pursuing
> the FPGA solution.
> 
> The only major drawback for NTSC machines would be the lack of artifacts for CoCo1/2 games,
> but an AD725 or similar could be added to generate high quality composite that might
> get them back on a secondary output.  Of course that doesn’t matter for PAL.
> 
> Very nice! :)
> 
> - Ed
> 
> 
> > On Oct 19, 2015, at 5:42 PM, Phill Harvey-Smith <afra at ramoth.org.uk> wrote:
> > 
> > On 19/10/2015 22:40, John W. Linville wrote:
> >> That's pretty cool, Phill!  After seeing the old Atom color boards
> >> I had thought to do a similar project at some point.
> >> 
> >> Do you have any plans to market such a board?
> > 
> > Well I'm thinking about it but got a couple of other projects on the go at the mo. And it's kinda still in development because of the PAL / NTSC thing.
> > 
> > Basically I'm maybe going to implement the PAL additional line logic in the CPLD so that it just relies on the VDG clock output by the SAM (and disconnects the 6847's VDG clock from any circuitry on the motherboard).
> > 
> > This should make it independent of the various different models of both the CoCo and Dragon motherboards, and as a side effect should enable a machine to run at either frame rate (if I get it right).
> > 
> > Cheers.
> > 
> > Phill.
> > 
> > -- 
> > Phill Harvey-Smith, Programmer, Hardware hacker, and general eccentric !
> > 
> > "You can twist perceptions, but reality won't budge" -- Rush.
> > 
> > -- 
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> > Coco at maltedmedia.com
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> 
> 
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-- 
John W. Linville		Someday the world will need a hero, and you
linville at tuxdriver.com			might be all we have.  Be ready.