XGA Common Information

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)
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?


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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Louis F. Ohland, Peter H. Wendt, David L. Beem, William R. Walsh, Tatsuo Sunagawa, Tomáš Slavotínek, Jim Shorney, Tim N. Clarke, Kevin Bowling, and many others.

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