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ModeLine-HOWTO by Rick Niles.
niles@axp745.gsfc.nasa.gov
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Version 1.0 2/11/95
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The file X11R6/lib/X11/doc/VideoModes.doc explains how to setup video
timings for your video card / monitor combination, however I found
this to be a long overly complicated explanation of something really
not that complex. Please let no one take offense at this, since
without this file I don't think I would ever have figured out how to
configure my setup and I am therefore very thankful to the writers of
that document. I just thought I would give my shortened explanation of
how to setup your XF86Config file for XFree86 and in particular
information about the Mach64 timings I've played with.
There are three major sections of the XF86Config file that deal with
the video card and monitor: the monitor section, the graphics device
section and the screen section. Ironically the timings I'm discussing
in this document concentrate on Monitor section even though I use
many specs from the video card.
In regard to the graphics device section I suggest commenting out any
"Clocks" given in the file when setting up a new server and/or video
card and let "X -probeonly" determine what Clocks are good for your
card / server combination. I recommend this above just putting in the
numbers given in the manual because exact timings on cards will vary.
Redirect this information into a file and copy it into the XF86Config
file.
Now the hard part about setting up a XF86Config file is the
definitions of the Modelines. For many non-ATI cards these number must
be multiples of 8. For ATI cards they need NOT be. There are 10
arguments after each Modeline directive:
Modeline <name> <DCL> <HR> <HPS> <HPE> <HFL> <VR> <VPS> <VPE> <VFL>
(name) Any name you'd like to assign to this mode, in double quotes.
The most common name is of the form HRxVR (e.g. "640x480")
However if you would like to have multiple Dot Clocks for a
give resolution setting your might try HRxVRxDCL
(e.g. "640x480x35.0")
(DCL) Dot Clock: This should be one of the dot clocks listed in the
manual or found in the Clocks section from the "X -probeonly"
command.
(HR & VR) Horizontal and Vertical Resolution: This also an easy one, it's
the number pixels you want to see across and down the
screen when you're in this mode.
(HPS, HPE, VPS, VPE) Hortz. & Vertical Pulse Start and End: This
controls where the image of the screen will be placed
relative to the physical screen. These are the numbers to
play with if the image is biased toward the edges of the
physical screen. For starters just make them evenly spaced
between the resolution numbers (HR,VR) and the field length
numbers (HFL,VFL).
If the image is biased toward the left (right), increase
(decrease) the HPS and the HPE.
If the image is biased toward the top (bottom), increase
(decrease) the HPS and the HPE.
(HFL,VFL) Horizontal & Vertical Field Length: Now these are the most
important numbers of all. If you set these numbers too
low or high for your monitor the XF86 server will reject
your whole modeline. The KEY relation to remember is:
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| DCL = HSF * HFL and DCL = RR * VFL * HFL |
---------------------------------------------
where HSF = Horiz. Scan Freq. (kHz)
RR = (Vert.) Refresh Rate (Hz)
These two numbers are given as a valid range for a particular monitor.
Try exceeding the specs and see how far you can go before funny
things start happening.
These two equations give you all the information you need to set up
your Modelines for a particular set-up. They leave two degrees of
freedom (i.e. two unknowns), for a chosen Dot Clock (DCL). As HFL and
VFL get smaller, the screen will get wider and taller. However, you
can not make these values arbitrarily close to the HR and VR since as
they approach these values the HSF and RR will exceed your monitor's
cabilities. Therefore one way of getting the maximum image size
(hence using the most of your physical monitor's real-estate) for a
particular Dot Clock (DCL) is to plug in the maximum HSF and RR your
monitor is rated for. If the image is still too small your only option is
to reduce the Dot Clock (DCL) (or try exceeding your monitor specs).
This fact troubled me for sometime as it seems counter-intuitive,
however try to get comfortable with it as it is true none-the-less.
The other way I thought of to resolve the extra degrees of freedom is
to use the video card table given in the manual of my Mach 64. The
manual gave DCL, HSF, & RR, hence I could solve for VFL & HFL using
the equations above. I thought this might be a good idea since perhaps
in some way the card was "designed" to work at these frequencies, and
hence they make work better in some way. (However, I now seriously
doubt that assumption.) Here is that table:
HFL and VFL values for XF86_Mach64 corresponding to ATI Mach64 Manual
Display Screen Refresh Horizon. Pixel Horizon. Vertical
Resolution Rate Freq. Clock Field Len. Field Len.
(pixels) (Hz) (kHz) (MHz) (Pixels) (Pixels)
(HRxVR) (RR) (HSF) (DCL) (HFL) (VFL)
-----------------------------------------------------------------
640x 480 60 31.5 25.2 800 525
640x 480 72 37.7 32.0 849 524
640x 480 75 37.5 35.0 933 500
640x 480 90 47.9 39.9 833 532
640x 480 100 53.0 44.9 847 530
800x 600 48 33.8 36.0 1065 704
800x 600 56 35.2 36.0 1023 629
800x 600 60 37.9 39.9 1053 632
800x 600 70 44.5 44.9 1009 636
800x 600 72 48.0 50.4 1050 667
800x 600 75 49.5 49.5 1000 660
800x 600 90 57.1 56.6 991 634
800x 600 100 62.5 67.5 1080 625
1024x 768 43 35.5 44.9 1265 826
1024x 768 60 48.3 65.0 1346 805
1024x 768 70 56.5 75.0 1327 807
1024x 768 72 58.2 75.0 1289 808
1024x 768 75 60.0 78.8 1313 800
1024x 768 90 76.2 100.0 1312 847
1024x 768 100 79.0 110.0 1392 790
1152x 864 43 45.9 65.0 1416 1067
1152x 864 60 59.0 80.0 1356 983
1152x 864 70 66.1 100.0 1513 944
1152x 864 75 75.1 110.0 1465 1001
1152x 864 80 80.0 126.0 1575 1000
1280x1024 43 50.0 80.0 1600 1163
1280x1024 47 50.0 80.0 1600 1064
1280x1024 60 64.0 110.0 1719 1067
1280x1024 70 74.0 126.0 1703 1057
1280x1024 75 80.0 135.0 1688 1067