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Old 12-01-2006, 12:41 PM   #1
Registered: Dec 2003
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Modeline for my LCD, please take a look - don't want to kill my LCD...

if I run "gtf 1600 1200 60 -v" the resulting modeline is:

# 1600x1200 @ 60.00 Hz (GTF) hsync: 74.52 kHz; pclk: 160.96 MHz
Modeline "1600x1200_60.00" 160.96 1600 1704 1880 2160 1200 1201 1204 1242 -HSync +Vsync

- what is the vertical frequency in there ? I think that it is the "160.96". My monitor is a Viewsonic 20 inch LCD using the DVI connection. When I look at its specs on the Viewsonic site the vertical refresh rate of 160.96 (assuming that this is what the number from the modeline is - the V refresh rate) is too high for my monitor and pretty much any LCD, I think.

Here is the way the Viewsonic site details the refresh range:
"VIDEO INPUT Analog RGB Analog (75 ohms, 0.7/1.0 Vp-p)
Digital DVI-D (TMDS, 100 ohms, or analog capable)
Frequency Fh: 30~92kHz, Fv: 50~85Hz
Sync H/V separated, composite, sync-on-green (TTL)"

Isn't that saying that the monitor should run somewhere in the range of 50 to 85 Hz for the Vertical refresh rate and not 160.96 ?!?!? The display looks good but I don't want to damage my monitor. I could use some advice, please.

Old 12-01-2006, 02:29 PM   #2
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Registered: Jul 2004
Location: Lower Rhine region, Germany
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I don't have gtf and don't know anything about it, but your interpretation of the Viewsonic site should be correct. If I were you I would manually edit /etc/X11/xorg.conf (if you use a recent distro that delivers xorg X server). Your monitor section should be similar to this:

Section "Monitor"

    Identifier  "viewsonic"
    # DPMS for energy saving
    Option      "DPMS"

# Viewsonic horizontal range
    HorizSync   30-92

# Viewsonic vertical refresh rate
    VertRefresh 50-85

Last edited by titopoquito; 12-01-2006 at 02:30 PM.
Old 12-01-2006, 03:08 PM   #3
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>if I run "gtf 1600 1200 60 -v" the resulting modeline is:>

># 1600x1200 @ 60.00 Hz (GTF) hsync: 74.52 kHz; pclk: 160.96 MHz
>Modeline "1600x1200_60.00" 160.96 1600 1704 1880 2160 1200 1201 1204 1242 -HSync +Vsy

>-what is the vertical frequency in there ? I think that it is the "160.96".

the vertical refresh frequency or sync rate is 60Hz, That is the number, 60, in the gtf command listed. should be fine for an LCD.

during each vertical scan 1200 horizontal lines need to be drawn and a few extras for CRTs to be able to sweep back to the top of the screen. 60 x 1200 gives 72KHz for the minimum horizontal rate. The number given 74.52KHz / 60 gives 1242 lines so 42 extra lines are provided for what is call vertical blanking. the 160.96MHz number is the pixel clock rate.

LCDs should not be damaged by wrong settings. In CRTs years ago the wrong frequencies would make high voltage transformers try to run at a frequency they were not designed for and they and the driver circuits could overheat. LCD drive is all low voltage stuff.
Old 12-01-2006, 04:21 PM   #4
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My LCD display just flashes "mode not supported" or something like that if it doesn't like what I'm sending it. One of these days, I'll have to hook this thing up to my Sony 50" LCD widescreen TV to see what happens.


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