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.This reduces the chance that you will damage your monitor bydriving it at a frequency which it was not designed for.The ModeLine directive is used to specify resolution modes for your monitor.Theformat isModeLine name clock horiz-values vert-valuesname is an arbitrary string which you will use to refer to the resolution mode later in thefile.dot-clock is the driving clock frequency, or dot clock associated with the resolutionmode.A dot clock is usually specified in MHz.It is the rate at which the video card mustsend pixels to the monitor at this resolution.horiz-values and vert-values are four numberseach that specify when the electron gun of the monitor should fire, and when the horizontaland vertical sync pulses fire during a sweep.The fileVideoModes.doc, included with the XFree86 distribution, describes in de-tail how to determine the ModeLinevalues for each resolution mode that your monitor 240 Advanced Featuressupports.clock must correspond to one of the dot clock values that your video card sup-ports.Later in theXF86Configfile, you will specify these clocks.Two files,modeDB.txtandMonitors, mayhaveModeLineinformation for yourmonitor.They are located in/usr/X11R6/lib/X11/doc.Start withModeLinevalues for VESA-standard monitor timings, because most mon-itors support them.ModeDB.txtincludes the timing values for VESA-standard resolu-tions.For example, this entry,# 640x480@60Hz Non-Interlaced mode# Horizontal Sync = 31.5kHz# Timing: H=(0.95us, 3.81us, 1.59us), V=(0.35ms, 0.064ms, 1.02ms)## name clock horizontal timing vertical timing flags"640x480" 25.175 640 664 760 800 480 491 493 525is the VESA-standard timing for a 640x480 video mode.It has a dot clock of 25.175,which your video card must support.This is described below.To include this entry in theXF86Configfile, use the lineModeLine "640x480" 25.175 640 664 760 800 480 491 493525The name argument to ModeLine ("640x480") is an arbitrary string.By conventionmodes are named by their resolutions, but name can, technically, be any descriptive label.For eachModeLine, the server checks the mode specifications and ensures that theyfall in the range of values specified forBandwidth,HorizSync, andVertRefresh.If they do not, the server complains when you attempt to start X.For one thing, the dot clockused by the mode should not be greater than the value used forBandwidth.However, inmany cases, it is safe to use a mode that has a slightly higher bandwidth than your monitorcan support.If the VESA standard timings do not work, (you ll know after you try to use them), thenlook in the files modeDB.txt and Monitors, which include specific mode values formany monitor types.You can createModeLineentries from these values as well.Be sureonly to use values for your specific monitor.Many 14 and 15-inch monitors do not supporthigher resolution modes, and often resolutions of 1024x768 at low dot clocks.If you can tfind high-resolution modes for your monitor in these files, then your monitor probably doesnot support them.If you are completely at a loss and can t find ModeLine values for your monitor,follow the instructions in the VideoModes.docfile, which is included in the XFree86 5.5.Configuring XFree86.241distribution, and generate values from the specifications in your monitor s manual.Yourmileage will certainly vary when you attempt to generateModeLinevalues by hand.Butthis is a good place to look if you can t find the values that you need.VideoModes.docalso describes the format of the ModeLine directive, and other aspects of the XFree86server in gory detail.Lastly, if you do obtain ModeLine values that are almost but not exactly right, youmay possibly be able to modify the values a little to obtain the desired result.For example,if the XFree86 display image is shifted slightly, or the image seems to roll, then followthe instructions in the VideoModes.doc file and fix the values.Be sure to check thecontrols on the monitor itself.In many cases, you must change the horizontal or verticalsize of the display after XFree86 starts, to center and size the image.3 Don t use monitor timing values or ModeLine values for monitors other than yourmodel.If you try to drive a monitor at a frequency for which it was not designed, you candamage or even destroy it.The next section of theXF86Configfile isDevice, which specifies parameters foryour video card.Here is an example.Section "Device"Identifier "#9 GXE 64"# Nothing yet; we fill in these values later.EndSectionThis section defines properties for a particular video card.Identifieris an arbi-trary, descriptive string.You will use this string to refer to the card later.Initially, you don t need to include anything in the Device section except theIdentifier.We will use the X server itself to probe for the properties of the videocard and enter them into theDevicesection later.The XFree86 server is capable of prob-ing for the video chip set, clocks, RAMDAC, and amount of video RAM on the board.Thisis described in Section 5.6.Before we do this, however, we need to finish writing the XF86Config file.Thenext section isScreen, which specifies the monitor/video card combination to use for aparticular server.Section "Screen"Driver "Accel"Device "#9 GXE 64"Monitor "CTX 5468 NI" 242 Advanced FeaturesSubsection "Display"Depth 16Modes "1024x768" "800x600" "640x480"ViewPort 0 0Virtual 1024 768EndSubsectionEndSectionTheDriverline specifies the X server that you will be using.ValidDrivervaluesare:Accel: For the XF86 S3, XF86 Mach32, XF86 Mach8, XF86 8514,XF86 P9000,XF86 AGX, andXF86 W32servers;SVGA: For theXF86 SVGAserver;VGA16: For theXF86 VGA16server;VGA2: For theXF86 Monoserver;Mono: For the non-VGA monochrome drivers in theXF86 MonoandXF86 VGA16servers.Be sure that/usr/X11R6/bin/Xis a symbolic link to this server
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