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Advanced BIOS Functions
DISPLAY REQUEST BLOCK
The display request block used in the Direct CRT I/O function contains control
data for the DMA exchange.
It
includes the command number, cursor position from
which the data is to be displayed, the number of characters to display, and the
addresses of the display data and attribute data buffers. Registers DS and DX are set
to the address of the display request block prior to issuing the function call. Figure
6-2 shows the format of the display request block.
CMD#
LA
CA
NOC
display data
offset
-----------
2 words (word boundary)
buffer
address
base
attribute data
offset
-----------
2 words (word boundary)
buffer
address
base
Figure 6-2 Display Request Block
CMD#:
LA,CA:
NOC:
o -
4 (command number)
Display/cursor position
LA (Line address)
=
0-24 binary, 1 byte
CA (Column address)
=
0-79 binary, 1 byte
Number of characters to be displayed
0-2000 binary, 1 word
6-19
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