When configured for MDA Mode 7, the display memory is organized into cells containing 2 bytes each. Byte 0 of each cell contains the 8 bit character code and byte 1 defines the display attributes for that character. Character cells are arranged in rows of 80 cells each, and there are 25 rows of cells. There is only one 80 x 25 page of text. The base address of display memory is B0000h and the size is 4000 bytes.
The attribute byte has the following bit definitions:
Only four foreground and background field combinations are useful:
Background Foreground Definition Field (hex) Field (hex) ============================================================================== 0 0 White on white (does not display) ------------------------------------------------------------------------------ x 1 Underlined characters ------------------------------------------------------------------------------ 7 0 Inverse video (white chars on black background) ------------------------------------------------------------------------------ 0 7 Normal video (black chars on white background) (*) ------------------------------------------------------------------------------(*) - Other combinations are also normal video.
