I have a DEC VRT19 connected to a PC, the connector panel in back of the =
monitor has solder pads for two extra BNC connectors, namely H and V =
sync. I simply fitted the two connectors and use a standard PC VGA to =
BNC cable. It also works under windows NT and 95 but obviously no VGA =
mode so you get lots of garbage during boot. It supports both 1024x768 =
at 85Hz and 1280x1024 at 75Hz.

Tony Parkinson
----------
From: 	David Burren
Sent: 	Tuesday, March 10, 1998 1:10 PM
To: 	Aaron J. Grier
Cc: 	Chris Jones; port-pmax@NetBSD.ORG
Subject: 	Fixed-freq monitors on PCs (was Re: PMAGB-J framebuffer =
support)

On Mon, 9 Mar 1998, "Aaron J. Grier" wrote:
> On Fri, 6 Mar 1998, Chris Jones wrote:

>> On a vaguely related note, does anybody know if there are video cards
>> out there for i386 machines that will do the necessary sync-on-green =
and
>> whatever else is necessary to support these old DECStation monitors?

There are cards available from several vendors which will support these
monitors under DOS/Windoze.  They have BIOSes which translate the
normal PC display modes into appropriate settings, and Windows drivers
to do the right thing in 95, NT, etc.

I've had reasonable success with some of these under NetBSD and FreeBSD
(as long as you don't try to play with 132-column modes).  Of course,
to drive them under XFree86 you need the right modeline...

In my mind the major drawbacks of these cards are:
	- You're limited to that vendor's choice of graphics engine.
	- They're expensive.

Another point to keep in mind is the monitor's refresh rate.  You may
have a nice 19" monitor, but if it only has a 60 Hz refresh, you might
not want to use it.  Some people don't realise this until they've spent
all their money...


> the easiest solution is probably just to make a
> convertor box.  I can personally vouch for the 4066 based circuit at
> http://www.paranoia.com/~filipg/HTML/REPAIR/F_Sync_Green3.html, as I =
use
> one with my PC running Xfree86 on a $40 Cirrus Logic video card =
driving
> an old Tektronix monitor...

I've had good success with converters built out of one resistor.  Crude
but effective.  My second model (and the one I still have) is a short
cable with VGA connectors at each end.  I use this in conjunction with
a standard VGA<->BNC cable to connect to any VGA card.  I can supply
the cable details tomorrow for anyone who's interested.  Right now I
can't remember details such as the resistor value :-)

I've had success with:
	Tektronix 16" and 19" Trinitron monitors
	HP A2094B
	DEC VRT19
	DEC VR297/299

Where I've used it the PC starts X in its rc, and up until then the
screen is unusable.  I'm happy with this setup because the PC is
essentially only an X display.  It boots diskless from a server, and if
it doesn't boot properly I can fix things from the server end.
Obviously YMMV...

This avoids the drawbacks I mentioned above:
	- I can use whatever VGA cards I have available.
	- It's cheap!
It offers no solution for DOS or Windows, but that's why I have a
WinCenter server :-)


>> For that matter, what *does* the video card have to do to work with =
one
>> of these monitors?
>
> Just has to have the sync timings right, and get the sync information =
on
> the green wire...

The other part of that is being able to output a high-enough
dot-clock.  If you're going to play with this stuff it helps to be
familiar with how that side of things works.  The XFree86 doco is
pretty good...

We now return you to your regularly scheduled pmax discussions :-)
__
David Burren
davidb@telstra.com.au