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Features of XGA/XGA-2
VGA Mode
132 Column Text Mode
Extended Graphics Mode
Direct Color Mode
8514/A Compatibility
Multiple XGA-2 Adapter Support MXGA, where are you?
Components of XGA-2
Display Controller
PS/2 Interface Controller
Memory and Cathode-Ray-Tube Controller
Video Coprocessor
Video Display Buffer
Serializer, Digital-to-Analog Convertor, and Palette
XGA2 Error Codes
XGA Datasheets
PC Graphics Handbook
Intro to XGA (INMOS)
INMOS XGA Software Programmer's Guide, Sep 91
INMOS Graphics Databook, 2nd Ed, 1990
INMOS G190 XGA Serializer Palette DAC 6-bit (XGA?)
INMOS G191 XGA Serializer Palette DAC 8-bit (XGA-2)
Tech Note Hardware Design with the INMOS G191
INMOS G200 XGA Display Controller (MCA)
INMOS G201 XGA Display Controller (MCA/ISA)
Features of XGA and XGA-2 Video Subsystems
VGA Mode
XGA/XGA-2 use a 32-bit data bus for all system memory and I/O
addresses. The VGA subsystem uses either an 8-bit or 16-bit data bus.
With a 16-bit data bus, XGA uses a 512KB video display buffer,
with a 32 bit data bus it uses a 1MB video display buffer. With a 32-bit
data bus, XGA-2 uses a 1MB video display buffer.
132 Column Text
Mode
VGA provides for an 80 character per line text mode. XGA/XGA-2
supports 132 characters per line on any display that has a vertical refresh
rate of 46.8 Hz interlaced or 59 Hz non-interlaced.
Extended
Graphics Mode
XGA/XGA-2 support 1024x768 by 256 colors. This mode supports
real and virtual memory addressing and multiple adapters in one computer.
Direct Color
Mode
Also known as palette bypass mode. With 1MB of VRAM, the direct color
mode provides 640x480 with 64k colors. VGA is limited to 256 colors.
8514/A
Compatibility
DOS AI makes the XGA/XGA-2 8514/A compatible at adapter interface level
and above.
Multiple XGA-2 Adapter
Support (MXGA)
194-255 OPTIONS BY IBM: MULTIMEDIA PRODUCTS
Multiple XGA Display Device Driver P/N 83G8292
You can install up to seven XGA-2 adapters in a MCA bus system
(limited by slot availability) or six if the XGA-2 is built into the planar.
When multiple adapters are used, they can do VGA or 132 column
text mode. However, VGA mode uses one set of addresses, and only one adapter
can use those addresses at a time. “Therefore, only one display at
a time can interact with the computer in the VGA mode or 132-column text
mode to change or refresh the image that it displays”.
Ed. What? What if all the adapters are in 132
column text mode?
Developed by a company in the UK
called Software 2000.
Components
of XGA-2
Consists of the display controller, video display buffer, serializer,
palette, and the digital-to-analog convertor (DAC).
Display
Controller
Consists of the PS/2 interface controller, memory and cathode-ray-tube
controller, and the video coprocessor.
PS/2
Interface Controller
This is the video interface to the microchannel bus. The controller
detects the bus width (16 or 32 bit) of the slot and prepares to transfer
data at that rate. It also acts as a busmaster that supports the video subsystem
(read adapter).
Memory
and Cathode-Ray-Tube Controller
This supports all VGA functions. It allows the system microprocessor
to access the video display buffer, and it controls the serializer and DAC.
Video Coprocessor
This is the key to the enhanced performance of the XGA-2 subsystem.
The coprocessor:
- Provides hardware drawing functions that can store
graphic data in both the video display buffer and system memory.
- Allows the video subsystem to become a 32-bit busmaster
that directly accesses system memory when in the extended graphics mode.
- Acts like a busmaster to other devices on the system
bus, such as another XGA-2 adapter, when in the extended graphics mode. It
can perform burst mode data transfers at up to 16.6MB per second.
- Updates memory independently of the system microprocessor,
which can then do other things while the coprocessor is drawing graphics.
- Supports virtual memory addressing.
- Rapidly suspends and resumes tasks (important in multiprocessing)
Video Display
Buffer
The buffer uses VRAM to store information that is being displayed.
VRAM allows data in the display buffer to be updated while the image on the
display is being refreshed.
1MB of VRAM provides faster performance in all video modes because
the data path into the video display buffer is 32 bits wide. With 512KB, the
data path is only 16 bits wide.
Serializer,
Digital-to-Analog Convertor, and Palette
The serializer and DAC convert the data in the video display buffer
to the imge you see on the screen.
The video data is stored in the video display buffer in 1-,
2-, 4-, 8-, or 16-bit units, known as pels. The number of bits per pel is
determined by the video mode that the computer is operating in. Each memory
location in the buffer holds one pel and corresponds to a specific location
on the screen. The binary value of each 1-, 2-, 4-, or 8-bit pel is used
as an index into the palette to determine the color that is to be displayed
at that location. If the computer is in the direct color mode, each pel is
16 bits, and it does not use the palette to determine the colors.
The serializer takes the data from the video display buffer and
converts it into a serial bit stream. If the pels are 1, 2, 4, or 8 bits,
the binary value of each pel corresponds to one of the 256 memory locations
in the palette. Each memory location contains 18 bits, divided into three
6-bit values that represent specific intensities of red, blue, and green.
In the direct color mode (palette bypass mode), each 16-bit pel is divided
into a 5-bit red intensity value, a 5-bit blue intensity value, and a 6-bit
green intensity value, for a total of 65,536 possible colors.
The DAC converts the digital color-intensity values to analog
values, which are more efficient than digital values for displaying the large
number of colors produced by high performance video. The DAC places the analog
values onto the display signal lines, and a colored dot is displayed on the
screen. Easy, right?
XGA/XGA-2 ERROR Codes
024318XX -- With the new revision of
the XGA-2 card (without a heat-sink on the processor chip), you may experience
a 024318xx error during the general function test of the XGA advanced diagnostics.
This is NOT a hardware failure, as indicated by the callout. There is
an incompatibility between the diagnostic program and the microcode on the
new processor chip on the XGA-2 card.
The solution is to download the new XGA-2 Option Diskette
from the BBS (XGA2ADP.EXE). This contains
the new version of the diagnostic for the XGA-2 card.
After updating IML, insure that you then backup the IML.
If the error shows up during post, or if there are problems
during the operation of the system, replace the XGA-2 card first.
Then if the problems persist, do the above procedure.
024374XX-- Copy an option has not successfully
completed. Copy XGA-2 Display Adapter/A option diskette to the backup
copy of the system programs/Reference Diskette; then run auto-configuration.
0243XXXX at POST-- Run Advanced Diagnostics
- Most likely will need to replace the XGA-2 Adapter/A.
If you get a message Error: Can not find file XGARING0.SYS upon bootup of
OS/2, you need to completely reinstall OS/2.
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