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Advanced BIOS Functions
6-20
dis pIa y data
buffer address:
attribute data
buffer address:
Starting address of display data buffer (offset, base
address; 2 words)
Starting address of attribute data buffer (offset, base
address; 2 words)
Figure 6-3 shows how the DMA transfer function works.
DISPL.A Y REQCEST BLOCK
--1
DISPLAY
DATA
VIDEO MEMORY
~
Il...
I
,
I
"
I
" ,
\
\
\
---------------
\
ARI,A
\"
;~
"
"
~
LA
I
CA
NOL
-r---.
-
,'----------
DMA TRANSHR
---
1111
I
41
I
00
I
42
I
DISPL\ Y DATA
[I'IDIO MIMORY H)RMA'I)
j
I',
~-----------,~--------------~
l
--
-----.~--------~
,'L-- . . . . . . .
I
- -
I
I
\
A TfRIBUTE
t- - -
- - - - - - - - - - - -
DMA TRANSII R
\T1RIHI'TID.YIA
DATA
AREA
\r-_
i
-------------,-~--------------~
__ 1 ____
->----1 _ _ I
Figure 6-3 DMA Transfer
The display request block contains the addresses of the display data area and the
attribute data area. On the video memory, each display character consists of two
bytes of display data and one corresponding byte of attribute data. The first byte of
the display data for each character identifies whether the following character code is
a normal character or an auxiliary character. The second byte of the display data is a
character code. The attribute data is a color code.
FIRST BYTE
SECOND BYTE
OOH= Normal
OOH through FFH
Display Data
89H = Auxiliary
Attribute Data
OOH = through FFH
N/A
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