Справочник Пользователя для AMD LX 800@0.9W
288
AMD Geode™ LX Processors Data Book
Display Controller
33234H
6.5.4
VGA Block Functional Overview
The VGA block provides full hardware support for a VGA
graphics subsystem. It is compatible with the IBM VGA as
defined in the IBM Video Subsystem Technical Reference
manual. This section provides an overview of VGA features
and functions.
graphics subsystem. It is compatible with the IBM VGA as
defined in the IBM Video Subsystem Technical Reference
manual. This section provides an overview of VGA features
and functions.
6.5.4.1
VGA Modes
A VGA “mode” is a programmed VGA configuration defined
by the VGA BIOS that produces a graphics frame buffer
format and a screen image with specific characteristics.
The base VGA function provides coded text modes for text-
based applications, and graphics modes for graphics-
based applications. Many of these modes are compatible
with older graphics adapter standards, such as mono-
chrome display adapter, color graphics adapter, and
enhanced graphics adapter.
by the VGA BIOS that produces a graphics frame buffer
format and a screen image with specific characteristics.
The base VGA function provides coded text modes for text-
based applications, and graphics modes for graphics-
based applications. Many of these modes are compatible
with older graphics adapter standards, such as mono-
chrome display adapter, color graphics adapter, and
enhanced graphics adapter.
Text Modes
There are five text modes defined by VGA BIOS as shown
Table 6-39.
Table 6-39.
Each of the text modes provides a coded frame buffer con-
sisting of a 16-bit value for each character. The low byte is
the ASCII character code for the character to display, and
the high byte is an attribute byte that determines how the
character is displayed (foreground, background colors,
blink, underline, etc.). There are two formats defined by
BIOS for the attribute byte: color and monochrome as
shown in Table 6-40.
sisting of a 16-bit value for each character. The low byte is
the ASCII character code for the character to display, and
the high byte is an attribute byte that determines how the
character is displayed (foreground, background colors,
blink, underline, etc.). There are two formats defined by
BIOS for the attribute byte: color and monochrome as
shown in Table 6-40.
Graphics Modes
The graphics modes defined by VGA BIOS are shown in
Table 6-41.
Table 6-41.
Figure 6-15. VGA Frame Buffer Organization
Table 6-39. VGA Text Modes
BIOS
Mode
#
Screen
Size in
Characters
Attribute
Type
Buffer
Address
Compatibility
0, 1
40 x 25
Color
B8000h-
BFFFFh
CGA
2, 3
80 x 25
Color
B8000h-
BFFFFh
EGA, VGA
7
80 x 25
Mono-
chrome
B0000h-
B7FFFh
MDA
Table 6-40. Text Mode Attribute Byte Format
Bit
Color Definition
Monochrome Definition
7
Blink
Blink
6
Background Color (R)
Background
5
Background Color (G)
Background
4
Background Color (B)
Background
3
Foreground Intensity/Font
Select
Select
Foreground Intensity/Font
Select
Select
2
Foreground Color (R)
Foreground
1
Foreground Color (G)
Foreground
Table 6-41. VGA Graphics Modes
BIOS Mode #
Screen Size in
Pixels
# of Colors
Frame Buffer
Format
Buffer Address
4, 5
320 x 200
4
Packed Pixel
B8000h-BFFFFh
6
640 x 200
2
Packed Pixel
B8000h-BFFFFh
0xD
320 x 200
16
Planar
A0000h-AFFFFh
0xE
640 x 200
16
Planar
A0000h-AFFFFh
0xF
640 x 400
4
Planar
A0000h-AFFFFh
0x10
640 x 350
16
Planar
A0000h-AFFFFh
0x11
640 x 480
2
Planar
A0000h-AFFFFh
0x12
640 x 480
16
Planar
A0000h-AFFFFh
0x13
320 x 200
256
Packed Pixel
A0000h-AFFFFh
3
2
1
0
Byte
Byte
Byte
Byte
64 KB
DWORDs