DEC Rainbow / Pro video on VGA monitors?

[Warner Losh]

On Sun, Jan 20, 2019 at 12:57 PM Marvin Johnston 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 can't remember the video output on the Rainbow, but I wanted to do
> something similar to have one setup for the S-100 machines. After
> looking on eBay (before I banned them from my use), I found a device
> that basically had RCA audio/video inputs with a VGA output. It also had
> the advantage of having an analog TV tuner built in so I could also use
> things like the old video games that had the Channel 3/4 output.
>
> The device is buried somewhere so I can't tell you the brand.
>

Yea. I'm going to order one or two others to see if I can get them to
work... The TRB says:

4.4.8.14 Composite Video Signal Characteristics
The composite video output provides a compatible EIA RS-170 output
generated by combining the video signal with a composite sync signal.

NOTE The use of dc coupling is not in strict agreement with the EIA RS-170
standard. To agree with RS170, the video generator output load would
require a 10 microfarad capacitor in series with the output. Without the
capacitor, the RS-170 2 milliamp dc short circuit requirement is violated.

The composite video output has the following nominal characteristics:
I. Output impedance = 75 ohms, dc coupled to 0.0 V
2. Sync level = 0.0 V
3. Reference black level = approximately 0.3 V with a 75 ohm load
4. Reference white level = approximately 1.0 V with a 75 ohm load
5. The composite sync waveform conforms to EIA RS-170 standards.

The vertical interval is composed of six equalizing pulses, six vertical
sync pulses, and six more equalizing pulses.

The timing is as follows:
Equalizing pulse width = 2.33us +/- 50ns
Vertical pulse width = 27.28us +/- 200ns
Horizontal pulse width = 4.71us +/- 50ns
Horizontal blank width = 11.84us +/- 50ns (80-column mode)
 = 12.34us +/- 50ns (132-column mode)
Front porch 1.54us +/- 50ns

This differs a little from what I've found online for RS-170 timings:

Reference Black = 0.075V
White = 1.00V
Sync = -0.40V

in some places but seems to correspond to the pics at
https://en.wikipedia.org/wiki/Composite_video almost exactly. So I'm
confused.

But I've seen other numbers as well. And the timings are roughly consistent
with the envelops suggested in an old terribly scanned doc from the 80's
that talks about video formats...

Anyway, video formats always proliferate into a cluster of almost the same
standards and it's hard to know what, exactly, to call them...

I'm not sure if this helped, or not :(

Warner