
82815 GMCH
R
Datasheet
119
3.8.2.
MSR
I/O (and Memory Offset) Address: 3C2h
Write;
Default:
Access:
Size:
7
Miscellaneous Output
3CCh
Read
00h
See Address above
8 bits
2
1
0
Reserved
A0000h
BFFFFh
Acc En
Reserved
Bit
Descriptions
7:2
Reserved
1
A0000
BFFFFh Access Enable.
VGA Compatibility bit enables access to the display cache at
A0000h
BFFFFh. When disabled, accesses to system memory are blocked in this region (by not
asserting DEVSEL#). This bit does not block processor access to the video linear frame buffer at other
addresses.
0 = Prevent processor access to the display cache (default).
1 = Allow processor access to display cache.
0
Reserved
3.8.3.
GR06
I/O (and Memory Offset) Address:
Default:
Access:
Size:
7
Miscellaneous Register
3CFh (Index=06h)
0Uh (U=Undefined)
Read/Write
8 bits
4
3
2
1
0
Reserved
Memory Map Mode
Reserved
Bit
Description
7:4
Reserved
3:2
Memory Map Mode.
These 2 bits control the mapping of the VGA frame buffer into the processor
address space as follows:
00 = A0000h
BFFFFh
01 = A0000h
AFFFFh
10 = B0000h
B7FFFh
11 = B8000h
BFFFFh
Note: This function is both in standard VGA modes and in extended modes that do not provide linear
frame buffer accesses.
1:0
Reserved