DEC Rainbow / Pro video on VGA monitors?

[Warner Losh]

On Sun, Jan 20, 2019, 4:11 PM Warner Losh <imp at bsdimp.com wrote:

> As a PS, I connected the real vr201 with a keyboard and got the attached
> photo. It looks like there is a one line error about missing keyboard in
> the first line when there is no keyboard. Counting out the rows on the boot
> screen confirms. So this is much closer than I thought.
>

The attached photo is actually the video on through the converter. Looks
like I left out that sentence, which was kinda important.

Warner
>
>
>
> On Sun, Jan 20, 2019, 3:16 PM Warner Losh <imp at bsdimp.com wrote:
>
>>
>>
>> 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
>>
>