AMD Geode LX 800@0.9W - Manual (Page 288)

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.
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.
Text Modes
There are five text modes defined by VGA BIOS as shown
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.
Graphics Modes
The graphics modes defined by VGA BIOS are shown in
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 Foreground Intensity/Font
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