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Monitor Adapter. The display buffer is configured at hex B8000.·
Bit image data is stored in bit plane O.
640x350 Monochrome Graphics (Mode F )
This mode supports graphics on the IBM Monochrome Display
with the following attributes: black, video, blinking video, and
intensified video. Resolution of 640x350 requires 56K bytes to
support four attributes. By chaining maps 0 and 1, then maps 2
and 3 together, two 32K bit planes can be formed. This chaining
is done only when necessary (less than 128K of graphics
memory). The first map is the video bit plane, and the second
map is the intensity bit plane. Both planes reside at hex address
AOOOO.
Two bits, one from each bit plane, define one picture element
(pel) on the screen. The bit definitions for the pels are given in
the following table. The video bit plane is denoted by CO and the
Intensity Bit Plane is denoted by C2.
C2
co
Pixel Color
Valid Attributes
0
0
Black
0
0
1
Video
3
1
0
Blinking Video
C
1
1
I ntensified Video
F
The byte organization in memory is sequential. The first eight
pels on the screen are defined by the contents of memory in
location AOOO:OH, the second eight pels by location AOOO: IH,
and so on. The first pel within anyone byte is defined by bit 7 in
the byte. The last pel within the byte is defined by bit 0 in the
byte.
Monochrome graphics works in odd/even mode, which means
that even CPU addresses go into even bit planes and odd CPU
addresses go into odd bit planes. Since both bit planes reside at
address AOOOO, the user must select which plane or planes he
desires to update. This is accomplished by the map mask register
of the sequencer. (See the table above for valid attributes).
IBM Enhanced Graphics Adapter 9
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