24 May
2020
24 May
'20
1:23 a.m.
-----Original Message-----
From: Tony Duell <ard.p850ug1 at gmail.com>
Sent: 24 May 2020 03:13
To: rob at jarratt.me.uk; Rob Jarratt <robert.jarratt at ntlworld.com>; General
Discussion: On-Topic and Off-Topic Posts <cctalk at classiccmp.org>
Cc: Paul Koning <paulkoning at comcast.net>
Subject: Re: Alternative Monitor for VAXmate
On Sat, May 23, 2020 at 10:49 PM Rob Jarratt via cctalk
<cctalk at classiccmp.org> wrote:
video
Err, no. The Pro (and Rainbow, DECmate II, etc) are TV rate. The horizontal
frequency is 15.57kHz or thereabouts. Those machines will work with TV-rate
video capture devices.
[...]
Tony, are you aware of any device I could buy or circuit I could build to get a decent
image out of it? It doesn't have to be perfect, but at least usable.
Thanks
Rob
The horizontal sync has a frequency of 26.6KHz, active
low with
the high voltage 3.7V, Vertical sync is 60Hz. I don't believe that
corresponds to any known standard, does it?
I assume it's the same as the Pro video. That might not exactly
match standards. But the intensity output is an acceptable 480i
monochrome signal. I've fed mine into a video capture
device and into a TV
display,
both
> work. I have wondered about RGB, the I/O board does
output an RGB signal
along with Intensity, Horizontal Sync and Vertical Sync, but I don't
know if I could feed that to a monitor that accepts RGB signals as I
don't know what the voltage levels should be. I have a VR241 which
seems to have suitable inputs but I don't know if I dare send the
signals from the I/O board straight to the VR241. I can't find a manual for it.
Again the VR241 is TV rate. The inputs are, I think, the normal 1V levels into
75ohms.
My experience is that sensible over-voltages on monitor inputs (e.g.
5V TTL signals into 1V analogue inputs) do no damage. It may not work, if it
does it may look terrible, but it won't let the magic smoke out.
-tony