On Sat, 25 Dec 1999, you wrote:
> Declan Moriarty wrote:
> >
> > I don't know the card, but I'm very surprised it only has a hsynch of
> > 31.5 - 35.5. You might just squeeze a satisfactory 800 x 600, but you'd be
> > better off staying with 640 x 480 and 60 Hz
>
> I changed it to 31.5-50 but with bad result, i'll keep trying.
If I were trying that, I would give it an extra few khz at a time. Go to 30-38;
if that works but you're still not happy, go to 40, etc.
>
> > I would imagine you would have at least 50Khz max refresh, not 35.5.
> > Your Gentleman on IRC probably had a very poor monitor. If the card has more
> > than 1 Mb of video ram, I would start again with the settings- they would have
> > to be wrong.
>
> Sure, and also because i don't really understand what is the real
> meaning of horizontal/vertical sync.
>
Right. The card has to give out something the monitor will see. Are the monitor
settings the limiting factor? What are your monitor settings?
Horizontal synch is the frequency at which the monitor writes one line
horizontally. Multiply vertical lines by the refresh (say, 60 Hz) gives you a
Horizontal synch.
Now multiply that by the 800 and the result by 1.25 gives you the DAC
speed. The 1.25 in that is an approximation; it allows for the unseen part of
the sweep, and the return time. Take my modeline here
Modeline "1024x768" 84.99 1024 1096 1272 1328 768 786 796 810
1024= r/h edge of visible portion; 1096 = r/h edge including unseen portion;
1272 = l/h edge - the time between 1096 & 1272 is for the return sweep; 1328 =
the end of the unseen l/h portion. So if you divide 1328 by 1024, the actual
approximation should have been 1.296. The 84.99(Mhz) is the DAC, which is the
speed at which the dot is written. My refresh (Vertical synch) is about 79 Hz.
(Divide 84.99Mhz by 1328, and the result by 810). 810 x 79 = 63.9Khz horizontal
synch.
Probably all the above is crap, but someone will correct it.
>
> sax detected DAC(?) as: 81. ram size is 2MB.
>
Right. 81Mhz divided by 65 max Vertical speed (It was 65Hz on your card,
wasn't it?) would give you 124khz. Is your monitor ancient?
Try an interlaced mode (The refresh doubles, and flicker would go) . Sax also
tells me the frequencies for the monitor, and card. With a DAC of 81 Mhz, your
card must be up to it. 31 - 35.5 looks like a monitor spec to me. I've never
seen a card that limited, and I've had some lousy ones!
One other thing to watch out for is that some cards don't support variable DAC
speeds, so you need to set the dac as well. This is a real pain. The Avance
Logic 2302 is an example. I never got it happening under X, as if the mode
needed a DAC of 32.51 Mhz and the card had 32.5, & 33Mhz as the available
steps, the mode got deleted!
--
Regards,
Declan Moriarty
