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VGA timing information

This documents tries to collect together information about standard VGA card timing details.

Information form HP monitor manual

Horizonal Timing

Horizonal Dots         640     640     640        
Vertical Scan Lines    350     400     480
Horiz. Sync Polarity   POS     NEG     NEG
A (us)                 31.77   31.77   31.77     Scanline time
B (us)                 3.77    3.77    3.77      Sync pulse lenght 
C (us)                 1.89    1.89    1.89      Back porch
D (us)                 25.17   25.17   25.17     Active video time
E (us)                 0.94    0.94    0.94      Front porch

         ______________________          ________
________|        VIDEO         |________| VIDEO (next line)
    |-C-|----------D-----------|-E-|
__   ______________________________   ___________
  |_|                              |_|
  |B|
  |---------------A----------------|

Vertical Timing

Horizonal Dots         640     640     640
Vertical Scan Lines    350     400     480
Vert. Sync Polarity    NEG     POS     NEG      
Vertical Frequency     70Hz    70Hz    60Hz
O (ms)                 14.27   14.27   16.68     Total frame time
P (ms)                 0.06    0.06    0.06      Sync length
Q (ms)                 1.88    1.08    1.02      Back porch
R (ms)                 11.13   12.72   15.25     Active video time
S (ms)                 1.2     0.41    0.35      Front porch

         ______________________          ________
________|        VIDEO         |________|  VIDEO (next frame)
    |-Q-|----------R-----------|-S-|
__   ______________________________   ___________
  |_|                              |_|
  |P|
  |---------------O----------------|

Informations source

• 
  
• HP D1194A Super VGA Display & HP D1195A Erognomic Super VGA Display Installation Guide, Hewlett Packard

"VGA industry standard" 640x480 pixel mode

General characteristics

Clock frequency 25.175 MHz
Line  frequency 31469 Hz
Field frequency 59.94 Hz

One line

  8 pixels front porch
 96 pixels horizontal sync
 40 pixels back porch
  8 pixels left border
640 pixels video
  8 pixels right border
---
800 pixels total per line

One field

  2 lines front porch
  2 lines vertical sync
 25 lines back porch
  8 lines top border
480 lines video
  8 lines bottom border
---
525 lines total per field              

Other details

Sync polarity: H negative, V negative
Scan type: non interlaced.

Information source

• 
  
• Article "Re: VGA specifications ,where ?" posted 19 Nov 1997 to sci.electronics.design newsgroup by Jeroen Stessen

More VGA mode information

There are the 3 "standard" VGA modes that each VGA card is supposed to be able to do:

• 
  
• 640 x 350 x 70 is compatible with the old EGA mode, but on a VGA display.
  
• 640 x 400 x 70 is the MS-DOS text mode (when the computer is booting !).
  
• 640 x 480 x 60 is the default Windows(tm) graphics mode (16 colours !).

Their line frequency is exactly twice that of the NTSC television system, or almost twice that of the PAL television system. This makes it fairly easy to implement a VGA input on a television set that uses line doubling for the television signals so the line deflection already runs on 31 kHz.

The following timings come from a list of 82 different computer timings, and by now there will be even more. Some video cards even have variable timing (allowing the user to set width, height and shift...). The only standard is that there is no standard !

"640 x 350 (EGA on VGA)"    "640 x 400 VGA text"        "VGA industry standard"
Clock frequency 25.175 MHz  Clock frequency 25.175 MHz  Clock frequency 25.175 MHz
Line  frequency 31469 Hz    Line  frequency 31469 Hz    Line  frequency 31469 Hz
Field frequency 70.086 Hz   Field frequency 70.086 Hz   Field frequency 59.94 Hz

One line:                   One line:                   One line:
  8 pixels front porch        8 pixels front porch        8 pixels front porch
 96 pixels horizontal sync   96 pixels horizontal sync   96 pixels horizontal sync
 40 pixels back porch        40 pixels back porch        40 pixels back porch
  8 pixels left border        8 pixels left border        8 pixels left border
640 pixels video            640 pixels video            640 pixels video
  8 pixels right border       8 pixels right border       8 pixels right border
---                         ---                         ---
800 pixels total per line   800 pixels total per line   800 pixels total per line                             

One field:                  One field:                  One field:
 31 lines front porch         5 lines front porch         2 lines front porch
  2 lines vertical sync       2 lines vertical sync       2 lines vertical sync
 54 lines back porch         28 lines back porch         25 lines back porch
  6 lines top border          7 lines top border          8 lines top border
350 lines video             400 lines video             480 lines video
  6 lines bottom border       7 lines bottom border       8 lines bottom border
---                         ---                         ---
449 lines total per field   449 lines total per field   525 lines total
per field                                                           

Sync polarity: H positive,  Sync polarity: H negative,  Sync polarity: H negative,
               V negative                  V positive                  V negative
Scan type: non interlaced.  Scan type: non interlaced.  Scan type: non interlaced.                                                    

Information source

Jeroen H. Stessen kindly mailed this information for me to be added to this document at November 1997.

SuperVGA timing from NEC monitor manual

Horizontal :
                ______________                 _____________
               |              |               |
_______________|  VIDEO       |_______________|  VIDEO (next line)

___________   _____________________   ______________________
           |_|                     |_|
            B C <------D-----><-E->
            <----------A---------->


Vertical :
                ______________                 _____________
               |              |               |           
_______________|  VIDEO       |_______________|  VIDEO (next frame)

___________   _____________________   ______________________
           |_|                     |_|
            P Q <------R-----><-S->
            <----------O---------->

For VESA 800*600 @ 60Hz:

Fh (kHz) :37.88
A  (us)  :26.4
B  (us)  :3.2
C  (us)  :2.2
D  (us)  :20.0
E  (us)  :1.0

Fv (Hz)  :60.32
O  (ms)  :16.579
P  (ms)  :0.106
Q  (ms)  :0.607
R  (ms)  :15.84
S  (ms)  :0.026

Information source

• 
  
• NEC Multisync manual

Necessary timing information about VGA modes

Vertical timing information

Mode name          Lines   line    sync      back        active     front     whole frame
                   Total   width   pulse     porch        time      porch        period
                           (us)   (us)(lin) (us)(lin)  (us)  (lin)  (us)(lin)  (us)  (lin)

VGA 640x480 60Hz    525    31.78   63   2   953   30   15382  484   285    9   16683  525       
VGA 640x480 72Hz    520    26.41   79   3   686   26   12782  484   184    7   13735  520
VGA 720x400 70Hz    449    31.78   63   2  1016   32   12839  404   349   11   14268  449
VGA 720x350 70Hz    449    31.78   63   2  1811   57   11250  354  1144   36   14268  449
VGA 800x600 56Hz    625    28.44   56   1   568   20   17177  604         -1*  17775  625
VGA 800x600 60Hz    628    26.40  106   4   554   21   15945  604         -1*  16579  628
VGA 800x600 72Hz    666    20.80  125   6   436   21   12563  604   728   35   13853  666
IBM 640x480 75Hz    525    25.397  51   2   761   30   12292  484   228    9   13333  525
MAC 640x480 66Hz    525    28.57   86   3  1057   37   13827  484    28    1   14999  525

• 
  
• Active area is actually an active area added with 4 overscan border lines (in some other VGA timing tables those border lines are included in back and front porch)
  
• Note than when the active part of VGA page is widened, it passes by the rising edge of the vertical sync signal in some modes (marked with *)

Horizonal timing information

Mode name          Pixel      sync      back  active  front whole line
                   clock      pulse     porch  time   porch  period
                   (MHz)   (us)  (pix)  (pix)  (pix)  (pix)  (pix)

VGA 640x480 60Hz   25.175   3.81   96     45    646    13     800
VGA 640x480 72Hz   31.5     1.27   40    125    646    21     832
VGA 720x400 70Hz   28.322   3.81  108     51    726    15     900
VGA 720x350 70Hz   28.322   3.81  108     51    726    15     900
VGA 800x600 56Hz   36       2      72    125    806    21    1024
VGA 800x600 60Hz   40       3.2   128     85    806    37    1056
VGA 800x600 72Hz   50       2.4   120     61    806    53    1040
IBM 640x480 75Hz   31.5     3.05   96     45    646    13     800
MAC 640x480 66Hz   30.24    2.11   64     93    646    61     864

• 
  
• Active area is actually an active area added with 6 overscan border pixels (in some other VGA timing tables those border pixels are included in back and front porch)

Information source

• 
  
• Jere M鋕el? Software design for a video conversion equipment, Master's Thesis, Helsinki University of Technology,23. August 1994, Appendix B.1

Timing used in one VGA monitor tester product

The following timings are used in VTG-KIT VGA monitor tester kit sold my Data Sync Engineering.

Mode       Horiz  Vertical  Horiz  Vert  Horiz  HSYNC  Vertical VSYNC
           Dots   Lines     KHz    Hz    Sync   Pol    Sync     Pol

VGA-480     640   480       31.5   60    3.8 us  -      64 us    -
VGA-400     640   400       31.5   70    3.8 us  -      64 us    +
SVGA I      800   600       35.2   56    2.0 us  -      57 us    -
SVGA II     800   600       37.8   60    3.2 us  +     106 us    +
SVGA III    800   600       48.0   72    2.4 us  +     125 us    +
XGA        1024   768       48.5   60    2.0 us  -     124 us    -