592 lines
30 KiB
Plaintext
592 lines
30 KiB
Plaintext
I. Release notes
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II. Videotiming configuration tutorial
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*******************************************************************************
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I. Release notes:
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-----------------
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o before atempting to start X386 run the script:
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/usr/lib/X11/X386/etc/install.sh !!!
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(This is ISC's version, but look at it what really happens, and do the
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same for your OS)
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o if you start X11 form the console - vt, there MUST be a free /dev/vt??
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o VPIX will only run with a version of X11R4 that supports TCP/IP.
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o You cannot switch to a different virtual terminal using <Alt><F?> or
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any other key combination. Use <Ctrl><SysReq><F?> instead. ISC folks
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use by default <Alt><SysReq><F?>.
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o The hot key combination <Ctrl><Alt><Bksp> will kill the server with no
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questions asked.
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SCO notes:
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The SCO version has some minor flaws at present. But then again the OS
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and development system do too.
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o The screen may go blank after stopping the server. Hit enter a couple
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times or run 'clear'.
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o No shared library support unless you have the newest DevSys, 3.2.2.
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o The CAPS and NUM lock work but don't light up.
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o Check /usr/lib/X11/X386/README_SCO for more details.
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Jim Kelly
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uunet!microsoft!jimke
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SVR4 notes:
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o There may be problems with vt-switching
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******************************************************************************
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II. Videotiming configuration tutorial
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---------------------------------------
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(written by Chin Fang, fangchin@leland.stanford.edu)
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Content:
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1. Introduction
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2. Get'em now
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3. Some preliminaries
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4. Lets get to work
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1. Introduction
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X386 allows it's users to configure their video subsystem and thus encourages
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a near optimum use of existing hardware. If you would like to use X386
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but do not feel having enough understanding about the configuration process,
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then this tutorial should provide you with enough background after you go
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thru it.
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Since most 386 Unix systems' video subsystems compose of a multi-scanning
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type monitor and a SVGA, so only setup for this type subsystems is covered.
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2. Get'em now
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Before you start setting up X386 on your system, you need to collect a few
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data and facts first. They are the following:
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(1) your monitor's sync frequency ranges for both horizontal and vertical
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directions
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(2) your video adapter (SVGA) driving frequency bandwidth
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Sync frequency ranges are usually tabulated in your monitor's user's manual,
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under specification. SVGA's spec. in it's user's manual usually provides
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the driving frequency bandwidth (and/or clock timings available). If not, the
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best way is to use the TURBO Pascal program clock.exe to detect the available
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clock timings (driving frequencies). It has to be done eventually to write
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the X386 configuration file Xconfig, so you may wish to run it as soon as
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possible. (clock.exe is provided as part of X386 distribution, so is it's src)
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Note, some analog monitors like NEC 2A and one Parkard Bell 14" model,
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only provide discrete sync frequencies for both horizontal and vertical
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directions. They can be configured too, and the procedure is similar.
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Only difference is that your room for configuration is severely limited
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by the built-in monitor characteristics. SPECIAL CARE SHOULD BE TAKEN
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WHEN X386 IS CONFIGURED FOR SUCH MONITORS!!
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Another fact you may like to know is that your SVGA card may not employ
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crystals as sources of video driving frequencies. Instead, some newer
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boards have a chip, most likely voltage controlled, for providing driving
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frequencies. An example would be like Swan Technology's SVGA uses a VCO
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(voltage controlled oscillator). Still, clock.exe should be able to reveal
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how many driving frequencies (clock timings) are available from such a
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chip oscillator.
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Finally, it's nice to get to know your monitor's video bandwidth if
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you intend to use high resolution and to drive such resolution at a
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high driving frequency, say 65Mhz. This is not a part of X386
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config process. But knowing it will enable you make more intellgent
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choices sometimes.
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Video bandwidth together with the employed driving frequency may affect
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your display's quality (like sharpness for fine details). However, most of
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the time one can ignore this. More explainations will be given below.
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Video Bandwidth is also tabulated in monitor's spec sheet.
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3. Some preliminaries
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When we talk about display, it's always NECESSARY to consider three things
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together:
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(1) your monitor's sync frequency ranges for both horizontal and vertical
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(2) your video adapter's driving frequency bandwidth (from crystals for ex.)
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(3) your software's video hardware device driver.
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and to a lesser extend, your monitor's video bandwidth. But for now
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lets concentrate on the three mentioned above.
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The sync frequency ranges of your monitor together with your video
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adapter's bandwidth determines the ultimate resolution that you can
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use. But it's up to the driver to untap any potential of your
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hardware. Superior hardware combination without an equally
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competent device driver is a waste of money. On the other hand,
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having a versatile device driver but not so good hardware combo, at
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least one can explore the limit of them. This is the design
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philosophy of X386.
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4. Lets get to work
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How to determine a good resolution for your monitor? Please read the following
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Definition: screen refresh rate => it's the DRIVING clock frequency divided
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by the product of horizontal frame length and vertical frame
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length.
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Q. what is driving clock frequency?
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A. it's the oscillatory frequency of the crystal(on your
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video board) employed by your graphics software's video
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driver. For instance, if your driver uses 36 Mhz out of
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25 28 0 40 36 40 45 58
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32 36 31 35 50 48 33 65 (all in Mhz, for Sigma Legend)
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then the driving frequency is 36Mhz. Nothing else.
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This is the frequency used by the driver to determine
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how frequent to update (thus refresh) screen image.
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Q. What's frame length for horizontal and vertical directions?
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A. It's the number of clock ticks (measured in terms of the
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driving timing) for your monitor's electron gun to impart
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a beam of electrons onto the screen and sweep such a beam
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from left side of the tube to the right side and back.
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Similarly, for vertical direction, from bottom to top and
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back to bottom.
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Q. Why this has anything to do with resolution?
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A. A desired resolution in fact should be called the portion
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of frame length during which an electron beam creates visible
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image to your eyes! Any image is created with your eyes's
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retention and the fast moving electron beam sweeping across
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your monitor. At any instant, there is in fact ONLY ONE dot
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hitting the screen, but due to your eyes retention, you
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see a block of image.
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Now it should be helpful to look at two pictures to
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get better idea:
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_______________________
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| | A horizontal frame
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|->->->->->->->->->->-> | length is the time
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| )| required for an
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|<-<-<-<-<-<-<-<-<-<-<- | electron beam tracing
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| | a pattern as shown on
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| | left
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|_______________________|
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_______________________
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| ^ | A vertical frame
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| ^ | | length is the time
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| | v | required for an
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| ^ | | electron beam tracing
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| | v | a pattern as shown on
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| ^ | | left
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| | v |
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| ^ | |
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|_______|_v_____________|
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It is always helpful to think that the image on a
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screen is formed by an electron beam tracing in a
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zigzag pattern, ie, the beam moves left <-> right
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and at the same time up <-> down too.
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Q. So what does this have anything to do with screen refresh
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rate?
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A. By definition, one hertz (hz) is one cycle per second.
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So, if your horizontal frame length takes x ticks, ver.
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frame length takes y ticks, then to cover the entire screen,
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a rectangular area, takes x times y ticks. Since your
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driving frequency provides say N ticks per second by
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definition, then obviously your monitor's electron gun(s)
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can impart a dot on the screen and sweep it from left
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to right and back and from bottom to top and back (which
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takes total xy ticks) N/xy times/sec. This IS your
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screen's refresh rate! Because that's how many times your
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screen can be updated thus REFRESHED per second!
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Q. Why I have to know this?
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A. You need to understand this concept to "design" a
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good resolution which not only provides you a steady
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image, but also utilizes your hardware in a near
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optimum manner.
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Q. So how do I get a desired resolution?
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A. Simple! Jut look at your monitor's data sheet, normally
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part of your users' manual. Make sure it's type, ie.
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fixed frequency or multiscaning. The later is much
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flexible if not better.
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THE FOLLOWING DISCUSSION DOES NOT APPLY TO THE FORMER!!
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Then, use your horizontal max sync frequency, say 55khz
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try out the clock frequencies listed or detected by
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clock.exe. As an example, say for Sigma Legend, there is
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a 65 Mhz clock oscillatory driving frequency available.
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And from above assumption, your monitor can sync up to
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55 Khz in horizontal. To get max REFRESH rate and
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at the same time get non-interlaceness, do the following:
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Obviously, if your clock cycles only N times per second,
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and if your monitor electron beam syncs at x times per
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second, the using the definition of frame length above,
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you can only have so many horizontal frames per second:
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N/x, in our sample, it would be 65Mhz/55khz=1181 times.
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But due to VGA's hardware restrictions, you can only have
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multiple of eight number of frames per second in the
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horizontal direction. So round it off -> 1176.
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This represent the MINIMUM frame length that you can
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use. You can, of course, get longer frame length by
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using lower sync frequencies. In so doing, you may
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not be able to raise viewing resolution, but you WILL
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pay the price of lower refresh rate. Following the
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explainations below you will find out why. Assuming,
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of course, the same driving frequency is still used.
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Take 80 percent of this clock ticks, or 944 ticks for your
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viewing image. This is a rule of thumb! Don't ask why!
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Take 75% of 944 as your vertical ticks for viewable image,
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you have 708 ticks. A rule of thumb is 1.05 times of ticks
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should be the vertical frame length ->743 ticks. Here I
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implicitly assumed that you like the Golden ratio.
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Please note that Golden ratio is not a requirement
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at all.
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So your screen refresh rate is 65Mhz/1176*743=74.4 hz!
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THIS IS EXCELLENT! Don't settle on anthing less IF POSSIBLE!
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The image at this update rate (or screen refresh rate)
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WILL LOOK STEADY EVEN TO VIDEO CAMERAS! (well... I know
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in this case it is not likely. Please keep reading to
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find out why)
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And you got 944x708 to boot. Not bad at all! You
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can even improve it further to put it into almost 76 Hz
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by using the fact that your monitor in horz. direction
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ofen can sync at higher frequency then 55 khz by about
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2khz or so and the fact that in vertical direction,
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you can lower the frame length somewhat. (ie, take less
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than 75% of 944 in the example above)
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All this is simple arithematics and simple facts about
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oscilloscopes. No black magic at all!
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But MAKE SURE that your monitor electron guns can sync
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up to 76 Hz vertical. (NEC 4D CANN'T for instance. It
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goes only up to 75 Hz in vertical)
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Q. What else do I need to know?
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A. You need to know when and where to place sync
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pluses. Recall the two pictures above? Only part
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of the time required for tracing such a frame is used
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for displaying viewable image (ie. your resolution).
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Lets say for the horizontal direction, it takes H ticks
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to trace the frame, and h ticks for viewable data.
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Obviously, h < H by definition. For concretness, lets
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assume both start at the same instant as shown below:
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|___ __ __ __ __ __ __ __ __ __ __ __ __
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|_ _ _ _ _ _ _ _ _ _ _ _ |
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|_______________________|_______________|_____
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0 h H unit: ticks
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^ ^
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<----->
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s
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Now, we would like to place a sync plus of length s
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like shown above, ie, between the end of clock ticks
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for display data and the end of clock ticks for the
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entire frame. Why so? because if we can achieve
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this, then your screen image won't shift to the right
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or to the left. It will be where it supposed to be
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on the screen, covering squarely the monitor's viewable
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area.
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Q. But I don't know how to get sync plus's length s, what
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can I do about it?
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A. Because this is the only tricky part of configuration,
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I want to get you understand all basics first before
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I overwhelm you with jargons. Now let's talk.
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In general, we have to do a little trial and error for
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this part. But most of the time, we can safely assume
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that a sync plus is about 3.5 to 4.0 micro second in
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length, as documented in some monitors user's manual
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in the spec section.
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For concretness again, let's take 3.8 micro second to
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be s, which btw, is not a bad value to start with.
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Now, using the 65Mhz clock timing above, we know s is
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equivalent to 247 clock ticks (= 65x10**6 * 3.8 *10**(-6))
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[recall M=10**6, micro=10**(-6)]
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Go back to the picture above, how do we place the
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247 clock ticks as shown in the picture?
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Now it's time for you to get your calculator!
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Using our example, h is 944 and H is 1176. The difference
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between the two is 1176-944=232 < 247! Obviously we
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have to do some adjustment here. What can we do?
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The first thing is to raise 1176 to 1184, and lower 944
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to 936. Now the difference = 1184-936= 248. Hmm, closer.
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Next, instead using 3.8, we use 3.5 for calculating s;
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then, we have 65*3.5=227. Looks better. But 248 is not
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much higher than 227. It's normally necessary to have
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30 or so clock ticks between h and the starting value of s
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and the same for the ending value of s and H. AND they
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have to be multiple of eight! Are we stuck?
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NO! let's do this, 936%8==0, (936+32)%8==0 too. But
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936+32=968, 968+227=1195, 1195+32=1227. Hmm.. this looks
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not too bad. But it's not a multiple of 8, so lets
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round it up to 1232.
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But now we got ourself in another potential trouble,
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the sync plus is no longer placed right in the middle
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between h and H anymore. Happily, using our calculator
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we find 1232-32=1200 is also multiple of 8 and
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(1232-32)-968=232 corresponding using a sync plus of
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3.57 micro second long, still reasonable.
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In addition, 936/1232~0.76 or 76%, still not far from
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80%, so it should be all right.
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Furthermore, using the current horizontal frame length, we
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basically ask our monRPor`4o`sync at 52.7khz(=65Mhz/1232)
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which is within it's capability. No problems.
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Using rules of thumb we mentioned before, 936*75%=702,
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This is our new vertical resolution. 702*1.05=737, our
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new vertical frame length.
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Screen refresh rate = 65Mhz/(737*1232)=71.6 Hz. THIS
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IS STILL EXCELLENT! KEEP IT.
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Q. But did you forget about how to place sync plus in the
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vertical direction?
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A. I intentionlly did so. Let's deal one thing at a time.
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For vertical direction, we usually would like to place
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sync plus as shown below:
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|___ __ __ __ __ __ __ __ __ __ __ __ __
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|_ _ _ _ _ _ _ _ _ _ _ _ |
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|_______________________|_______________|_____
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0 v V unit: ticks
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^ ^
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<----->
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sv
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Note in the picture, we start the sync plus at the end
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of the vertical display data ticks. Since by the defintion
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of frame length, a vertical tick is the time for tracing a
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complete HORIZONTAL frame, therefore in our examlple, it
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is 1232/65Mhz=18.95us. Experience shows that a vertical
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sync plus should be in the range of 50us and 300us.
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As an example let's use 150us, which translates into 8
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vertical clock ticks (150us/18.95us~8).
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Q. Are we done already so far? I am tired!
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A. YES! we are almost done. All we need to do from now on
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is to write our result into Xconfig as follows:
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#name clock horizontal timing vertical timing flag
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936x702 65 936 968 1200 1232 702 702 710 737
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No special flag necessary. Now we are REALLY done.
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Q. Then what is the memory requirement for such a resolution?
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A. Memory requirment: 936x702/1024~642K video RAM. So if
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you have one meg, you have extra for virtual terminal
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switching. See, this is good compromise!
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However, if you only have 512K on board, then you can't
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use it. Even you have a good monitor, without enough
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video ram, you can't take advantage of your monitor's
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potential. On the other hand, if your SVGA has one meg,
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But your monitor can display at most 800x600, then high
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resolution is beyond your reach either. But the extra
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video ram can always be used for useful things like
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running multiple servers and virtual terminal switching
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Please read X386.man for details.
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Q. The example you gave is not a standard, can I use it?
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A. WHY NOT? There is NO reason whatsover why you have to use
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640x480, 800x600, or even 1024x768. X386 driver lets you
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config your hardware with a lot freedom. It usually takes
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two to three minutes to come up the right one.
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The KEY is high refresh rate with reasonable viewing area.
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NOT Hi Res at the price of flickerness!
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Q. It this the ONLY resolution given the two 65Mhz and 55Khz
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timings?
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A. ABSOLUTELY NOT!! You are encouraged to follow the general
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procedure and do some trial and error to come up a setting
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that's really to your liking. Believe me, it's fun.
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Furthermore, you need to read X386.man to see how to set
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up different resolutions for the server, and how to use
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hot key combos to chose them at run time. That way, you
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can setup different resolutions for different needs.
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Q. You mentioned video bandwidth earlier, why you have not
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discussed it yet?
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A. Because I don't think you can use it for your X386
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configuration. Most of the time you simply can ignore this
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monitor characteristics. With a SVGA and most hi res
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monitors, you CANN'T even reach the limit of your monitor's
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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video bandwidth. The following are examples
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Brand Video Bandwidth
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NEC 4D: 75Mhz
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Nano 9070 50Mhz
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Nano 9080i 60Mhz
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Mitsubishi HL6615 110Mhz
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Mitsubishi Diamon San 100Mhz
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IDEK MF-5117 65Mhz
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IOCOMM Thinksync-17 CM-7126 136Mhz
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HP D1188A 100Mhz
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Philips SC-17AS 110Mhz
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Most well known SVGA cards provide driving frequency ONLY
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up to 65Mhz. So obviously, judging from above samples,
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video bandwidth is not a factor you need to worry about.
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Q. Then why almost all monitor makers are making a big fuss
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about it? And what it is anyway?
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A. Simply put, your monitor employes electronic signals
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to represent data (or image to your eyes). Such signals
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always come in in wavy form once they are converted into
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analog form from digitized form. They can be considered
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as combinations of many simpler wave forms each one of
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which has a fixed frequency, many of them are in the Mhz
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range, eg, 20Mhz, 40Mhz, or even 70Mhz. Your monitor
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video bandwidth is the capability of it's internal circuts
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|
to process such high frequency signals without distorting
|
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their forms.
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|
So, if a monitor has a board bandwidth, like CM-7126
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|
listed above, then clearly any signal containing components
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having frequencies lower than 136Mhz would come thru it's
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circuits with their wave form intact. Other models can
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not claim so.
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Consequently, fine details of images can be displayed
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without lossing fidelity. Shapeness is thus maintained.
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|
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I emphasize that video bandwidth is just one factor in
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getting high quality image. There are other things to
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be considered as well. For more info, consult your
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librarian.
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Q. But I don't have a pricy hi-res monitor. Mine is only
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a humble NEC Multisync II, should I care?
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|
A. Still NO! NEC Multisync II can't even display 800x600
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|
per it's spec. It can only display 800x560. For such
|
|
a low resolution, you never need any high clock timing
|
|
provided by your SVGA, most likely you can only use
|
|
32Mhz and 36Mhz, both of them are still not too far from
|
|
the monitor's rated video bandwidth 30Mhz.
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|
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|
At these two driving frequencies, your screen image may
|
|
not be as shape as it should be, but definitely of tolerable quality. Of course it would be nicer if NEC Multisync II
|
|
had a video bandwidth higher than, say, 36Mhz. But this
|
|
is not critical for common tasks like text editing, as long
|
|
as the difference is not significant so as to cause severe
|
|
image distortion (if so your eyes would tell you right away).
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|
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|
If you only want 640x480, then only 25Mhz or 28Mhz are
|
|
good choices. Both of which are lower than 30Mhz. So you
|
|
are even safer in this case.
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|
|
|
Q. You just mentioned two standard resolutions. In Xconfig,
|
|
there are many standard resolutions available, can you tell
|
|
me whether I still need to "tinker" with X386's config?
|
|
A. Absolutely! Take, for example, the "standard" 640x480
|
|
listed in the current Xconfig. It employes 25Mhz driving
|
|
frequency, frame lengths are 800 and 525 => refresh rate
|
|
~ 59.5Hz. Not too bad. But 28Mhz is a commonly available
|
|
driving frequency from many SVGA boards. If we use it to
|
|
drive 640x480, following the procedure we discussed above,
|
|
you would get frame lengths like 812 and 505. Now the
|
|
refresh rate is raised to 68Hz, a SIGNIFICANT improvement
|
|
over the standard one! Your eyes will tell you if you
|
|
don't trust my words.
|
|
|
|
Q. I don't believe your emphasis on refresh rate! Using your
|
|
definition, I got like 45Hz but I feel fine.
|
|
A. Owing to the geometry of our pupils, when you face your
|
|
monitor, and if you are using a dark background, with
|
|
a good constrast for foreground color, and low to medium
|
|
intensity, you shouldn't feel too bad even at 45Hz.
|
|
|
|
The acid test is this: open a xterm with pure white back-
|
|
ground and black foreground using xterm -bg white -fg black
|
|
and make it so large as to cover the entire viewable area.
|
|
Now turn your monitor's intensity to 3/4 of it's setting,
|
|
and turn your face away from the monitor. Try peeking at
|
|
your monitor sideways. If you don't sense any flicker or
|
|
if you feel the flickering is tolorable to you. Then that
|
|
refresh rate is fine with you. Otherwise you better do
|
|
something about it.
|
|
|
|
Different individuals have different sensitivity/tolerance
|
|
to flickering. Above 60Hz is HIGHLY recommanded. Remember
|
|
even florescent lights are refreshed at 60Hz, we still often
|
|
use them in clusters to reduce flickering?
|
|
|
|
Q. But how about interlace/non-interlace?
|
|
A. The key word in video watching is NON-FLICKER! The point
|
|
is that non-interlace is just part of the game! With non
|
|
interlace alone BUT low screen refresh rate, your eyes will
|
|
suffer badly!!!! Interlace-ness just worsen the flickering
|
|
at the same refresh rate. If you can manage to get high
|
|
enough refresh rate, say 90 Hz for interlace display, you
|
|
WILL NOT feel any flicker!! (But I doubt this is feasible)
|
|
|
|
So, CONCLUSION => NON-INTERLACENESS != NON-FLICKER!
|
|
|
|
Q. Can you summarize what we have discussed so far?
|
|
A. Sure! It would be:
|
|
|
|
(1) for any fixed driving frequency, raising max resolution
|
|
incurs the penalty of lowering refresh rate and thus
|
|
introducing more flickering.
|
|
(2) if a high resolution is desirable and your monitor
|
|
supports such, try to get a SVGA card that provides
|
|
a matching high driving frequency. The higher, the
|
|
better!
|
|
|