9th Pixel of 9x16 VGA Fonts Mimics 8th Pixel for ASCII 192-223 (59953)

SUMMARY

The width of CGA, EGA, MCGA, and VGA text characters is 8 pixels. In the case of VGA however, 9 pixels are actually used for displaying the characters. The 9th pixel is appended to the right end of each pixel row. If the character being displayed has an ASCII code ranging from 192 to 223 and the 8th pixel in a given pixel row is on, the 9th pixel in that row will be on also. If the 8th pixel in the row is off or the ASCII code for the character is not in the range 192 to 223, the 9th pixel will not be turned on.

This hardware information may be of interest to users of Microsoft QuickBasic Versions 4.00, 4.00b, and 4.50 for MS-DOS, Microsoft Basic Compiler Versions 6.00 and 6.00b for MS-DOS and MS OS/2, and Microsoft Basic Professional Development System (PDS) Version 7.00 for MS-DOS and MS OS/2.

MORE INFORMATION

The following diagram shows the pixel make-up of a sample VGA character and how it would be displayed on the screen if it had an ASCII code within the range 192 to 223, and if its ASCII code was also outside that range:

   * = lit pixel
   O = unlit pixel

   Pixel make-up        ASCII 192             ASCII 255
   -------------        ---------             ---------

   OO****OO             OO****OOO             OO****OOO
   O******O             O******OO             O******OO
   ********             *********             ********O
   ********             *********             ********O
   ********             *********             ********O
   ********             *********             ********O
   ********             *********             ********O
   ********             *********             ********O
   ********             *********             ********O
   ********             *********             ********O
   ********             *********             ********O
   ********             *********             ********O
   ********             *********             ********O
   ********             *********             ********O
   O******O             O******OO             O******OO
   OO****OO             OO****OOO             OO****OOO

Note how the 9th pixel mimics the status of the 8th pixel preceding it when the ASCII code is 192. When the ASCII code is 255 (outside the range 192 to 223), the 9th pixel is always off, regardless of the status of the 8th pixel. This behavior is limited to VGA text mode and is not found in CGA, EGA, or MCGA.