Справочник Пользователя для AMD LX 800@0.9W
360
AMD Geode™ LX Processors Data Book
Display Controller Register Descriptions
33234H
6.6.18.6 VGA Character Map Select
Character Map A (bits [5,3:2]) and Character Map B (bits [4,1:0]) determine which font tables are used when displaying a
character in text mode. When bit 3 of the character's attribute = 1, Character Map A is used; when bit 3 of the character's
attribute = 0, Character Map B is used. The font tables are stored in the 64 KB in map 2. There are eight font tables. The
character map codes select the font tables as shown in Table 6-52.
character in text mode. When bit 3 of the character's attribute = 1, Character Map A is used; when bit 3 of the character's
attribute = 0, Character Map B is used. The font tables are stored in the 64 KB in map 2. There are eight font tables. The
character map codes select the font tables as shown in Table 6-52.
6.6.18.7 VGA Memory Mode
Index
03h
Type
R/W
Reset Value
xxh
VGA Character Map Select Register Bit Descriptions
Bit
Name
Description
7:6
RSVD
Reserved. Write as read.
5
CHAR_AZ
Character Map A bit 2.
4
CHAR_BZ
Character Map B bit 2.
3:2
CHAR_A
Character Map A bits 1:0.
1:0
CHAR_B
Character Map B bits 1:0.
Table 6-52. Font Table
Code
Font Table Location in Map 2
Code
Font Table Location in Map 2
0
8 KB Block 0
4
8 KB Block 1
1
8 KB Block 2
5
8 KB Block 3
2
8 KB Block 4
6
8 KB Block 5
3
8 KB Block 6
7
8 KB Block 7
Index
04h
Type
R/W
Reset Value
02h
VGA Memory Mode Register Bit Descriptions
Bit
Name
Description
7:4
RSVD
Reserved.
3
CHAIN4
Chain4. When set to a 1, CPU address bits 1 and 0 are used to select the map or plane
in the frame buffer DWORD. For example, if CPU A1:A0 = 3, then map 3 is selected. If
CPU A1:A0 = 1, then map 1 is selected. If Chain4 is 0, then the frame buffer addressing
is controlled by the CHAIN2 (bit 2).
in the frame buffer DWORD. For example, if CPU A1:A0 = 3, then map 3 is selected. If
CPU A1:A0 = 1, then map 1 is selected. If Chain4 is 0, then the frame buffer addressing
is controlled by the CHAIN2 (bit 2).
2
CHAIN2
Chain2. When set to a 0, CPU address bit 0 selects between frame buffer maps 0 and 1,
or maps 2 and 3, depending on the value in the graphics controller Read Map Select field
(Index 04h[1:0]). For example, if CPU A0 is 0, then map 0 (or 2) is selected.
or maps 2 and 3, depending on the value in the graphics controller Read Map Select field
(Index 04h[1:0]). For example, if CPU A0 is 0, then map 0 (or 2) is selected.
1
EXT_MEM
Extended Memory. This bit should always be set to a 1. It is a throwback to EGA where
the standard frame buffer size was 64 KB and was upgradeable to 256 KB. VGA always
has (at least) 256 KB.
the standard frame buffer size was 64 KB and was upgradeable to 256 KB. VGA always
has (at least) 256 KB.
0
RSVD
Reserved.