From: dogbowl@dogbox.acme.gen.nz (Kennelmeister)
Subject: Re: Atari Mono and VGA
Reply-To: dogbowl@dogbox.acme.gen.nz (Kennelmeister)
Organization: The Dawghaus BBS, Palmerston North, New Zealand (+64 6 357 9245)
Lines: 52

arosborn@oregon.uoregon.edu (Alan Osborn) writes:

> In article <1993Apr19.090707.3686@tdb.uu.se>, m88max@tdb.uu.se (Max Brante) w
> >Have anybody succeded in converting a atari monomchrome monitor into a
> >mono VGA monitor. If so please let me know exactly how you did and what
> >graphics card you used.

> I wish I could help!  I posted a similar question about two weeks ago;
> I got no response at all.  I've asked locally at my friendly Atari store.
> I was told that it should be possible, but that they had no idea how
> it might be done.  Nor did they particularly care to investigate.

OK, here's my results so far....

1: You have to define the monitor as LCD - it doesn't really support
   Analogue video input (It works, but isn't very linear...)

2: The incoming sync pulses need inverting. This is best achieved
   with either a cmos XOR package or a transistor inverter.
   If you don't know how to do it, don't even contemplate it.. :-)

3: It'll only work in standard VGA mode.

OK, having said that, I'm trying to either find a circuit or IC
which will act as a universal sync decoder.

I want somethikng which basically only detects the leading sync
pulse edge, and doesn't care about the polarity, outputting
the -ve going pulses that the atari monitor requires.

There are 2 reasons for doing this

1: VGA cards change their sync polarity depending which mode they're
   in - herc emulation is +,- while MVGA is +,+ for example.

2: It means I don't have to put a toggle switch on the back of the
   monitor in order to be able to run it off both the atari and my
   IBM. Currently I have 3 (Yes, 3!) monitors sitting on my desk,
   and I want to get that number down as much as possible.
   Being able to use the atari monitor as a paper-white VGA
   will cut things down to 2. If I forget about Atari colour,
   I can get down to 1.

Ultimately, the best course of action is to get a multisync monitor,
but I'm as pressed for cash as anyone else, so it'll have to wait...



--
Alan Brown
dogbowl@dogbox.acme.gen.nz