DEC Rainbow / Pro video on VGA monitors?
paulkoning at comcast.net
Sat Dec 28 13:57:25 CST 2019
> On Jan 19, 2019, at 4:38 PM, Paul Koning <paulkoning at comcast.net> wrote:
>> On Jan 19, 2019, at 1:57 PM, Warner Losh via cctalk <cctalk at classiccmp.org> wrote:
>> I'm trying to find a way to get my DEC Rainbow's monochrome output onto a
>> newer monitor than my aging VR201 (especially since I zapped something in
>> it and my diagnostic efforts to date haven't fixed it).
> I'd be interested in the answer also, for my Pro.
Digging in old email...
I've looked at this some more the other day. Two observations.
1. The "mono" video output from the Pro is a valid composite video signal, no surprise there.
2. For color signals, the approach I'm going to try in the near future is to convert to "component video". That's a trivial analog process, see https://www.analog.com/en/design-center/reference-designs/circuit-collections/lt6550-rgb-to-ypbpr-component-video-conversion.html for example.
The reason this seems like a good approach is that component video inputs of typical TV sets support "480i" signals, which is what the Pro produces. Contrast that with VGA, which is effectively 480p (no interlace, 2x the horizontal frequency) so producing that is a much harder job.
If you can change the color mapping, you could even just feed an RGB signal directly to a component video input, with G going to Y (assuming you have sync on green) and R/B going to Pr/Pb with a bias in the color map entries to make the result right. Haven't tried that either.
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