ddcprobe, which needs to be run as root, will give you information about your monitor. Here is the output for the monitor I am using on one of my VL boxes:
root:# ddcprobe
VESA 2.0 detected.
OEM Name: ATI RADEON 9200
Memory installed = 256 * 64k blocks = 16384kb
Supported standard modes:
800x600x16
1024x768x16
320x200x32k
320x200x64k
320x200x16m
1600x1200x256
640x400x256
640x480x256
640x480x32k
640x480x64k
640x480x16m
1600x1200x32k
800x600x256
800x600x32k
800x600x64k
800x600x16m
1600x1200x64k
1024x768x256
1024x768x32k
1024x768x64k
1024x768x16m
1280x1024x256
1280x1024x32k
1280x1024x64k
1280x1024x16m
132x25 (text)
132x43 (text)
EDID ver. 1 rev. 1.
Manufacturer: XXX
ID: 6550
EISA ID: XXX6550
Serial number: 031a8695.
Manufactured in week 35 of 2004.
Input signal type: analog signal.
Screen size max 32 cm horizontal, 25 cm vertical.
Gamma: 2.600000.
DPMS flags: RGB, active off, suspend, standby.
Established timings:
640x480 @ 60 Hz (VGA)
640x480 @ 75 Hz (VESA)
800x600 @ 60 Hz (VESA)
800x600 @ 72 Hz (VESA)
800x600 @ 75 Hz (VESA)
1024x768 @ 75 Hz (VESA)
Standard timing 0: 85 Hz, 640x480
Standard timing 1: 85 Hz, 800x600
Standard timing 2: 85 Hz, 1024x768
Standard timing 3: 85 Hz, 1280x1024
Standard timing 4: 60 Hz, 1600x1200
Standard timing 5: 75 Hz, 1600x1200
Monitor details 0:
Timing ranges: horizontal = 30 - 96, vertical = 50 - 150
Monitor details 1:
Name: 1996F
Monitor details 2:
Serial number: 0434452070037
Detailed timing 3:
Pixel clock: 2570000
Horizontal active time (pixel width): 257
Horizontal blank time (pixel width): 1
Vertical active time (pixel height): 257
Vertical blank time (pixel height): 1
Horizontal sync offset: 257
Horizontal sync pulse width: 1
Vertical sync offset: 1
Vertical sync pulse width: 0
Dimensions: 257x1
With the information given to me by ddcprobe, when I run one of the text-mode X configuration tools, I'll use the following for the horizontal and the vertical sync ranges:
Monitor details 0:
Timing ranges: horizontal = 30 - 96, vertical = 50 - 150
Here is the corresponding section of my xorg.conf file with that information:
Section "Monitor"
# HorizSync is in kHz unless units are specified.
# HorizSync may be a comma separated list of discrete values, or a
# comma separated list of ranges of values.
# NOTE: THE VALUES HERE ARE EXAMPLES ONLY. REFER TO YOUR MONITOR'S
# USER MANUAL FOR THE CORRECT NUMBERS.
# HorizSync 30-64 # multisync
# HorizSync 31.5, 35.2 # multiple fixed sync frequencies
# HorizSync 15-25, 30-50 # multiple ranges of sync frequencies
# VertRefresh is in Hz unless units are specified.
# VertRefresh may be a comma separated list of discrete values, or a
# comma separated list of ranges of values.
# NOTE: THE VALUES HERE ARE EXAMPLES ONLY. REFER TO YOUR MONITOR'S
# USER MANUAL FOR THE CORRECT NUMBERS.
Identifier "My Monitor"
HorizSync 30.0 - 70.0
VertRefresh 50.0 - 150.0
EndSection
I chose to go a bit more conservative in my horizontal sync number, but things work well for me.
HTH a bit,
John