INT 10H 0cH: Write Graphics Pixel

                                                          Compatibility: All 
 Expects: AH    0cH
          AL    color number (+80H means XOR with current value)
          BH    video page (0-based)
          CX    graphics column
          DX    graphics row
 Returns: (none)
    Info: Even on the FASTEST computers, this fn is WAY TOO SLOW to expect
          to get any reasonable amount of drawing done.

          The BIOS does not support line-drawing or other standard graphics
          primitives.  To draw graphics with reasonable speed, you must
          access video memory directly.  See Video Memory Layouts.

   Notes: When you add 80H to the color value in AL, the specified color is
          XORed with the color that is currently at that position.  That is
          a useful graphics operation since XORing the same value twice
          ends up with the original value.

See Also: INT 10H 0dH (read graphics pixel)
          INT 10H: Video Services