VGA Timings

The following table lists timing values for several popular resolutions.

Note: SM Modes 0-13 only

As with RS-232, the standard for VGA video is that there are lots of standards. Every manufacturer seems to list different timings in the manuals for their monitors. The values given in the table above are not particularly critical. On a CRT monitor, the lengths of the front and back porches control the position of the image on the display. If the image appears offset to the right or left, or up or down, try adjusting the front and back porch values for the corresponding direction (or use the image position adjustments on the monitor, which accomplish the same thing).

• 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)

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

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.                                                    

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

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    -