On the EGA and MCGA, the bits of BL are used as follows:Determines the character blocks selected by bit 3 of character attribute bytes in alphanumeric (text) display modes.
Call with:
AH = 11H
AL = 03H
BL = character generator block select code (see Notes)
Returns:
Nothing
Notes:
On the EGA and MCGA, the bits of BL are used as follows:
Bits Significance 0—1 character block selected by attribute bytes with bit 3 = 0 2—3 character block selected by attribute bytes with bit 3 = 1 4—7 not used (should be 0)
On the VGA, the bits of BL are used as follows:
Bits Significance 0,1,4 character block selected by attribute bytes with bit 3 = 0 2,3,5 character block selected by attribute bytes with bit 3 = 1 6—7 not used (should be 0)
When using a 256-character set, both fields of BL should select the same character block. In such cases, character attribute bit 3 controls the foreground intensity. When using 512-character sets, the fields of BL designate the blocks holding each half of the character set, and bit 3 of the character attribute selects the upper or lower half of the character set.
When using a 512-character set, a call to Int 10H Function 10H Subfunction 00H with BX = 0712H is recommended to set the color planes to eight consistent colors.