NetNews Usenet Archive 1992 #30/NN_1992_30.iso/spool/comp/windows/x/i386unix/57

Text File | 1992-12-21 | 2.7 KB | 62 lines

Newsgroups: comp.windows.x.i386unix
Path: sparky!uunet!munnari.oz.au!metro!news
From: [e-mail] (David Dawes)
Subject: Re: [Help] Xfree86, Trident, interlace
Message-ID: <[e-mail]>
Sender: [e-mail]
Nntp-Posting-Host: physics.su.oz.au
Organization: School of Physics, University of Sydney, Australia
References: <[e-mail]>
Date: Fri, 18 Dec 1992 14:52:35 GMT
Lines: 49

In article <[e-mail]> [e-mail] (Gerhard Fuernkranz) writes:
>My configuration:
>
>    - Xfree86-1.1 running under Linux
>    - SVGA card with Trident 8900C chip, 1MB ram
>    - NEC 3D monitor
>
>The video modes 640x480, 800x600 and 1024x768 work fine in
>non-interlaced mode. But, due to the limitations of my monitor
>(max. 38kHz horizontal frequency) I use a dot clock of 45 MHz
>for 1024x768, which results in a vertical frequency of below
>50 HZ (I'll get woozy, when I have to look at the screen for a longer
>time).
>
>So I tried to design an interlaced video mode. I used the modegen
>spreadsheet, that is available under Linux to compute the parameters.
>I used a dot clock of 36 MHz, which results in a vertical frequency
>of about 43 Hz (which should be 86 Hz in interlaced mode),
>wrote the resulting configuration values from the spreadsheet into
>the Xconfig file an put the keyword `interlace' at the end of the line.
>
>My monitor syncs, both horizontally and vertically, but the first of
>the two half-pictures appears on the top half of the screen and the
>second one on the bottom, i.e. everything is drawn twice and with the
>half height. There also is a horicontal gray stripe between the
>two pictures, which seems to be the v-sync, that is produced by the
>VGA card between the two half-pictures.
>The flickering picture lets me believe, that the monitor syncs at
>43 Hz (i.e. every 2nd v-sync pulse) instead of 86 Hz.
>I also tried to to put `[+-][vh]sync' into the Xconfig file, but
>it did not influence the behaviour.
>
>N.B.: Interlaced 1024x768 mode works fine under DOS and with
>      Linux' tvgalib.
>
>Does anybody know, what's going on or what I have made wrong ?
>Are there special timing requirements for interlaced modes ?

I have an et4000 card and NEC 3D.  I run 1024x768 interlaced with a 45 MHz
clock.  The mode setting I use is:

"1024x768i" 45    1024 1064 1224 1264    768  777  785  817   Interlace

David
--
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 David Dawes ([e-mail])    DoD#210      | Phone: [phone]
 School of Physics, University of Sydney, Australia   | Fax:   [phone]
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