AMD Geode LX 800@0.9W - Manual (Page 375)

AMD Geode™ LX Processors Data Book 375
Display Controller Register Descriptions 33234H
6.6.20.5 VGA Color Compare
Bits [3:0] specify a compare value that allows the CPU to compare pixels in planar modes. Read mode 1 performs a com-
parison based on these bits combined with the Color Don’t Care bits. Data returned will contain a 1 in each one of the eight
pixel positions where a color match is found. See the description of read modes (Section 6.5.5.4 on page 291) for more
information.
6.6.20.6 VGA Data Rotate
Index 02h
Type R/W
Reset Value xxh
VGA Color Compare Register Bit Descriptions
Bit Name Description
7:4 RSVD Reserved.
3 CO_CM_MP3 Color Compare Map 3.
2 CO_CM_MP2 Color Compare Map 2.
1 CO_CM_MP1 Color Compare Map 1.
0 CO_CM_MP0 Color Compare Map 0.
Index 03h
Type R/W
Reset Value xxh
VGA Data Rotate Bit Descriptions Bit Descriptions
Bit Name Description
7:5 RSVD Reserved.
4:3 WROP Write Operation. Data written to the frame buffer by the CPU can be logically combined
with data already in the CPU data latches.
00: Copy (CPU data written unmodified).
01: CPU data ANDed with latched data.
10: CPU data ORed with latched data.
11: CPU data XORed with latched data.
See the description of write modes (Section 6.5.5.3 on page 290) for more information.
2:0 ROTCNT Rotate Count. This value is used to rotate the CPU data before it is used in write modes
0 and 3. The CPU data byte written is rotated right, with low bits wrapping to the high bit
positions. See the description of write modes (Section 6.5.5.3 on page 290) for more
information.