[Coco] CoCo3 RBG Video Questions

David Ladd davidwladd at gmail.com
Thu May 28 16:32:49 EDT 2020

On Thu, May 28, 2020 at 2:51 PM Frank Thompson <frank.thompson.iv at gmail.com>

> Hi Everyone!
> Based on some searches of past messages, I saw a tip about using a video
> scaler to adapt the 15kHz RGB video signal from the CoCo3 to a standard VGA
> monitor.
> I purchased the scaler mentioned in these postings, an Extron DVS 304.  I
> have some unusual behavior that I'm trying to isolate to determine who is
> at fault:  the CoCo, my homemade RGB to DB15 cable, or the Extron unit.
> So, to start, it took some fiddling with the knobs of the Extron to get it
> to work, but now that it is set up, it is AMAZING.  The video signal is
> just gorgeously clean and crisp.  (By the way, if anyone wants to know the
> fiddling I needed to do to get it to work, let me know.  It is not relevant
> to this present discussion so omitted).
> I can boot up CoCo3 specific games in RGB mode and the video is awesome.
> I've launched Robocop, Predator, Rescue on Fractulus, and FlightSim II.
> However, some older games (not all) show up in a poor looking (fuzzy, but
> legible) black and white screen.  Examples include Pitfall II and even my
> Gamepak based Hunt the Wumpus.
> I confirmed that the composite video out of the RCA jack on the back of the
> CoCo is showing in proper color (hooking directly from CoCo to monitor).

The older CoCo 1, 2, and Dragon games that use NTSC artifacting will not
work on RGB. Composite and over the air formats were the only way to get
the artifacting cause of the way NTSC worked.  True RGB outputs do not get
the artifacting from NTSC.  Which is why CoCo 3 people back in the day when
they got their CM-8 monitors could not play the old PMODE 4 artifacting

That is just the way things worked back then.  So what you are expecting is
not a fault of the scaler or the cables.  Just the type of video output you
want doesn't come from the RGB.

That is where people normally keep composite monitors or TV's around so
they can still see the artifacting.

> I'm not sure if the issue is with the video scaler, the CoCo, or those
> games just aren't usable with RGB monitors (I'm not sure why that would be
> but I don't know the hardware).  If it is the fault of the scaler, does
> that imply that there is a difference in the signals out of the CoCo RGB
> port for the different games and the scaler just can't handle certain
> differences?
> Again, as a tangent, I can post more of my details of getting the Extron to
> work (not much to it really) if people are interested.
> Thanks all!
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