Unfortunately the "few weeks' training you get from programming the VGA
chips on most display boards is worth less than nothing because it's
consuming too much time and effort and using time which could be used in
more valuable pursuits. I can assure you that soldering a resistor onto the
back of a display adapter is sufficient to verify that the monitor can be
used, and no programming of any sort is needed. If the card is capable of
60 Hz non-interlaced 1280x1024x256-color display, programming it won't be
necessary, as it will support that format. If it's not, all the programming
either of us could do won't help.
The sync mixer I have used, and instructed others to use, many times since
the mid-to-late '80's is quite simple, uses a current mirror, a dif-amp, and
a couple of diodes configured as a negative logic OR, with the aid of a half
dozen resistors. It's a circuit any first year EE student should be able to
build and fully understand. If the first year EE student can do it, so can
anyone else! It was probably designed by a student and then cleaned up by
the guys at Brooktree, from one of whose app-notes I pinched the circuit
back in days of old. I had to add details about the hookup, but it's
essentially their circuit. The benefit is that it will happily tolerate
either polarity of one or the other sync signals if you fiddle with it a
bit.
I'd not consider trying to program this display format in to a board which
doesn't normally support it because that normally indicates it isn't
capable. You might want to get out your slide rule and figure out how fast
the pixels have to fly out of the DAC if you want 1280 of them in the active
portion of a 64kHz sweep. Most of them (the boards in question) simply
won't do that.
Dick
-----Original Message-----
From: Tony Duell <ard_at_p850ug1.demon.co.uk>
To: Discussion re-collecting of classic computers
<classiccmp_at_u.washington.edu>
Date: Tuesday, July 20, 1999 1:05 PM
Subject: Re: Sun Monitor (UK) (2)
>>
>> Having had a while to recall, I believe the SONY, formerly attached to a
SUN,
>> did, indeed, have five BNC inputs on it. However, in order to get the
>> display board and the monitor to "play" together, it was easier to use
only
>> three of them because, in the absence of SYNC on the last two BNC's it
>> happily responded to negative-going sync on GREEN. I'm not sure whether
>
>This is certainly going to be a YMMV thing, so I think it's best if I
>make my comments as well, and whoever is trying to get the monitor
>working can pick which one they prefer...
>
>I prefer to use separate syncs where possible. For one thing it
>eliminates the sync mixer and separator stages. For another, it gives me
>nice simple signals to trigger a 'scope off when I have problems.
>
>Inverting a TTL signal (particularly one < 1MHz) is IMHO a lot easier
>than making a sync mixer which has to handle video signals aproaching
>100MHz. Still, it's up to you.
>
You're right, it is easier, but this circuit is already designed and proven.
It simply needs to be built faithfully to the schematic and such that it
looks good. So long as there are no excessively long (meaning longer than
absolutely necessary) wires, and so long as the soldering is neat and clean,
everything should go well.
>
>> All the points you've made are well considered, which is why I suggested
you
>> start with the resistor to green just to see whether you can use this
>> monitor with the cards you own. It's really not worth the effort to make
a
>> card not already capable of the right scan rates do the job if you have
to
>> reinvent the display board's BIOS, as that vendor in southern California
>> does. At 50 cents per hour, the effort will approach the national debt.
A
>> really decent 19" monitor compatible with most any current VGA card costs
>> $400 at the Best-Buy or whatever other discount store you like. There is
a
>> point beyond which even I, frugal as I am, won't wander.
>
>You've forgotten the education you'll get doing this :-). You'll learn
>about programming VGA chips, working with video/sync signals, maybe
>getting inside the monitor and tweaking the scan rates, etc.
>
at $1(US) per hour you'll save a fortune by buying a good 20" monitor at a
computer store. You'd be better off shining shoes for it than trying to
program a board which doesn't already do what you want.
>
>Or at least that's how I justify spending a few weeks mending something
>when I could buy one for a few pounds down at the local PC shop :-)
>
Don't they say, "penny-wise, pound-foolish" where you live?
>
>-tony
>
Received on Tue Jul 20 1999 - 17:06:08 BST