VT8601 Apollo ProMedia
Revision 1.3 September 8, 1999
-85
VGA Extended Registers
7HFKQRORJLHV ,QF
:H&
:H&RRQQHFW
QQHFW
VGA Extended Registers – Graphics Controller Indexed
GRE – Old Source Segment Address...............................RW
7-3
Reserved
........................................ always reads 0
2-1
Source Segment Address Select .............. default = 0
0
Reserved
........................................ always reads 0
GRE – New Source Segment Address..............................RW
7
Reserved
........................................ always reads 0
6-0
Source Segment Address Select .............. default = 0
Bit-1 is written inverted
GRF – Miscellaneous Extended Function Control ........ RW
7
Reserved
........................................ always reads 0
6
Character Clock Division Control Bit-1 (see bit-3)
00 No division ............................................ default
01 Divide by 2
10 Divide by 3
11 -reserved-
5
Symmetric / Asymmetric DRAM Address
0
Symmetric.............................................. default
1
Asymmetric
4
Compressed Chain 4 Mode for CPU Path
0
Disable................................................... default
1Enable
3
Character Clock Division Control Bit-0 (see bit-6)
2
Alternate Bank & Clock Select
0
Disable 3D8, 3D9, and 3xB................... default
1
Enable 3D8, 3D9, and 3xB
1
Compressed Chain 4 Mode Display Path
0
Disable................................................... default
1Enable
0
Source Segment Address Register Enable
0
Disable GRE.......................................... default
1Enable GRE
All bits except 2 and 0 are write protected by SRE_New[7]
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