On Tue, 12 May 1998 19:41:19 -0700 (PDT)  "Aaron J. Grier" wrote:

> On Wed, 13 May 1998, Toru Nishimura wrote:
> 
> > It would make you much happier to obtain a decent "multi-sync PC
> > monitor"  with BNC connectors behind it.  High end PC monitors take two
> > inputs with BNC and HD Dsub15.  You could use them interchangably
> > between PCs and DECstations, and save space/electoricity/what-so-ever. 
> 
> True, but high-end PC monitors are terribly expensive, and don't most
> PC-style monitors with BNC connectors expect their sync signals on
> separate lines?
> 
> I've been wondering lately about how one would convert a sync-on-green BNC
> system to a VGA DB15.  [1] I've been thinking of setting up some kind of
> resonant circuit (PLL or otherwise) to sync up to both the H and Vsync
> pulses, and then send those directly to the proper pins on the DB15, but
> if the impedances on the monitor are high enough, shouldn't it be possible
> to take the green BNC connector and hook it to the green and sync
> connectors on the VGA DB15?  Will the green input on the monitor be blown
> by seeing a +5V sync pulse?  (A quick acting video switch should take care
> of that.)  Will the monitor get confused by seeing Hsync pulses on the
> Vsync line and vice versa?

I've got a Digital VRC21 (or VRC20?  I'm home right now) on my desk that
has a VGA cable coming out of it.  Attached to that is a DEC-supplied
"convertor" with a female DB15 at one end and BNC sockets on the other
end.  There doesn't appear to be any circuitry of any kind and certainly
no power requirements.  I've been happily using the monitor on both a
3100 (1024x864) and a PMAGB-B (1280x1024).

Certainly when I bought a fixed-frequency PC video card a couple of
years ago so I could use a Sony GDM-1950, the company I bought the
card from supplied instructions to build a BNC sync-on-green to DB15
connector - it was just a resistor which tied horizontal and vertical
sync to green.  I constructed the thing on a pair of icy-pole sticks to
keep the bare wires apart, and it worked fine until I threw the video
card out.  I'll dig up the info if anyone wants it.

Simon.