IBM RT Series Hardware Reference Manual page 408

The IBM Monochrome Display and Printer Adapter supports 256
different character codes. In the character set are alphanumerics
and block graphics. Each character in the display buffer has a
corresponding character attribute. The character code must be an
even address, and the attribute code must be an odd address in
the display buffer.
7
6 5 4 3 2 0
Character Code
Even Address (M)
7
6 5 4 3 2 0
Bl
I
R
I
G
I
B
I
I
I
R
I
G
B
I Attribute Code
Odd Address (M
+
1)
I
I I I
~
Foreground
Intensity
Background
Blink
The adapter decodes the character attribute byte as defined
above. The blink and intensity bits may be combined with the
foreground and background bits to further enhance the character
attribute functions listed below:
Background Foreground
R G
B
R G
B Function
0
0
0 0 0 0 Non-Display
0 0 0
0 0 1 Underline
0 0 0 1 1 1 White Character/Black Background
1 1 1 0 0 0
Reverse Video
The 4K display buffer supports one screen of the 25 rows of 80
characters, plus a character attribute for each display character.
The starting address of the buffer is hex BOOOO. The display
buffer can be read using direct memory access (DMA); however,
at least one wait state will be inserted by the system unit's
microprocessor. The duration of the wait state will vary, because
the microprocessor/monitor access is synchronized with the
character clock on this adapter.
6 Monochrome Adapter