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specs/freevga/vga/vga.htm
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specs/freevga/vga/vga.htm
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<HTML>
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<HEAD>
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<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
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<META NAME="Author" CONTENT="Joshua Neal">
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<META NAME="Description" CONTENT="Pure VGA/SVGA hardware programming (registers, identification, and otherlow-level stuff.)">
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<META NAME="KeyWords" CONTENT="VGA SVGA hardware video programming">
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<TITLE>VGA/SVGA Video Programming--Standard VGA Chipset Reference</TITLE>
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</HEAD>
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<BODY>
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<CENTER><A HREF="../home.htm">Home</A> <A HREF="#intro">Intro</A> <A HREF="#general">General</A>
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<A HREF="#register">Registers</A> <A HREF="#index">Index</A> <A HREF="../home.htm#vga">Back</A>
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<HR WIDTH="100%"><B>Hardware Level VGA and SVGA Video Programming Information
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Page</B></CENTER>
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<CENTER>VGA Chipset Reference
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<HR WIDTH="100%"></CENTER>
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<UL>
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<LI>
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<A HREF="#intro">Introduction</A> -- introduction to the VGA reference</LI>
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<LI>
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<A HREF="#general">General Programming Information</A> -- details of the
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functional operation of the VGA hardware.</LI>
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<LI>
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<A HREF="#register">Input/Output Register Information</A> -- details on
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the VGA registers themselves</LI>
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<LI>
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<A HREF="#index">Indices</A> -- convenient listings of fields and their
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locations alphabetically and by function</LI>
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</UL>
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<A NAME="intro"></A><B>Introduction</B>
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<BR> This section is intended
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to be a reference to the common functionality of the original IBM VGA and
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compatible adapters. If you are writing directly to hardware then this
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is the lowest common denominator of nearly all video cards in use today.
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Nearly all programs requiring the performance of low-level hardware access
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resort to this baseline capacity, so this information is still valuable
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to programmers. In addition most of the VGA functions apply to SVGA cards
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when operating in SVGA modes, so it is best to know how to use them even
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when programming more advanced hardware.
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<BR> Most VGA references I have
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seen document the VGA by describing its operation in the various BIOS modes.
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However, because BIOS was designed for use in MS-DOS real mode applications,
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its functionality is limited in other environments. This document is structured
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in a way that explains the VGA hardware and its operation independent of
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the VGA BIOS modes, which will allow for better understanding of the capabilities
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of the VGA hardware.
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<BR> This reference has grown
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out of my own notes and experimentation while learning to program the VGA
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hardware. During this process I have identified errors in various references
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that I have used and have attempted to document the VGA hardware's actual
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behavior as best as possible. If in your experience you find any of this
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information to be inaccurate, or even if you find this information to be
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misleading or inaccurate, please let me know!
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<BR> One of the reasons I started
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this reference was that I was using existing references and found myself
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wishing for a hypertext reference as almost every register is affected
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by the operation of another, and was constantly flipping pages. Here I
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simply use links for the register references, such as <A HREF="crtcreg.htm#13">Offset
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Register</A>, rather than stating something like: Offset Register (CRTC:
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Offset = 13h, bits 7-0). While the second method is more informative, using
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them for every reference to the register makes the text somewhat bogged
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down. HTML allows simply clicking on the register name and all of the details
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are provided. Another is that no single reference had all of the information
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I was looking for, and that I had penciled many corrections and clarifications
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into the references themselves. This makes it difficult to switch to a
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newer version of a book when another edition comes out -- I still use my
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heavily annotated second edition of Ferarro's book, rather than the more
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up-to-date third edition.
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<P><A NAME="general"></A><B>General Programming Information</B>
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<BR><B> </B>This section is intended
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to provide functional information on various aspects of the VGA. If you
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are looking simply for VGA register descriptions look in the next section.
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The VGA hardware is complex and can be confusing to program. Rather than
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attempt to document the VGA better than existing references by using more
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words to describe the registers, this section breaks down the functionality
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of the VGA into specific categories of similar functions or by detailing
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procedures for performing certain operations.
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<UL>
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<LI>
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<A HREF="vgamem.htm">Accessing the VGA Display Memory</A> -- details on
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the memory interface between the CPU and VGA frame buffer.</LI>
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<LI>
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<A HREF="vgaseq.htm">Sequencer Operation</A> -- details on how the VGA
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hardware rasterizes the display buffer</LI>
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<UL>
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<LI>
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Text-mode</LI>
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<UL>
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<LI>
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<A HREF="vgatext.htm">VGA Text Mode Operation</A> -- details concerning
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text mode operation, including attributes and fonts.</LI>
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<LI>
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<A HREF="textcur.htm">Manipulating the Text-mode Cursor</A> -- details
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controlling the appearance and location of the cursor.</LI>
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</UL>
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</UL>
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<UL>
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<LI>
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<A HREF="vgafx.htm">Special Effects Hardware</A> -- details on hardware
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support for windowing, paging, smooth scrolling and panning, and split-screen
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operation.</LI>
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</UL>
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<LI>
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<A HREF="vgaattr.htm">Attribute Controller Operation</A> -- details on
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the conversion of sequenced display data into DAC input. <B>(WIP)</B></LI>
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<LI>
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<A HREF="vgadac.htm">DAC Operation</A> -- details controlling the conversion
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of palette data into analog signals.</LI>
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<LI>
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<A HREF="vgacrtc.htm">Display Generation</A> -- details on formatting of
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the produced video signal for output to the display.</LI>
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</UL>
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<A NAME="register"></A><B>Input/Output Register Information</B>
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<BR> This section is intended
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to provide a detailed reference of the VGA's internal registers. It attempts
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to combine information from a variety of sources, including the references
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listed in the reference section of the home page; however, rather than
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attempting to condense this information into one reference, leaving out
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significant detail, I have attempted to expand upon the information available
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and provide an accurate, detailed reference that should be useful to any
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programmer of the VGA and SVGA. Only those registers that are present and
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functional on the VGA are given, so if you are seeking information specific
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to the CGA, EGA, MCGA, or MGA adapters try the Other References section
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on the home page.
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<BR> In some cases I have changed
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the name of the register, not to protect the innocent but simply to make
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it clearer to understand. One clarification is the use of "Enable" and
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"Disable". A the function of a field with the name ending with "Enable"
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is enabled when it is 1, and likewise a field with a name ending in Disable
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is disabled when it is 1. Another case is when two fields have similar
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or identical names, I have added more description to the name to differentiate
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them.
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<BR> It can be difficult to understand
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how to manipulate the VGA registers as many registers have been packed
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into a small number of I/O ports and accessing them can be non-intuituve,
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especially the Attribute Controller Registers, so I have provided a tutorial
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for doing this.
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<UL>
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<LI>
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<A HREF="vgareg.htm">Accessing the VGA Registers</A> -- methods of
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manipulating the VGA registers</LI>
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</UL>
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In order to facilitate understanding
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of the registers, one should view them as groups of similar registers,
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based upon how they are accessed, as the VGA uses indexed registers to
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access most parameters. This also roughly places them in groups of similar
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functionality; however, in many cases the fields do not fit neatly into
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their category. In certain cases I have utilized quotes from the IBM VGA
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Programmer's Reference, this information is given in "<I>italic.</I>"
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This is meant to be a temporary placeholder until a better description
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can be written, it may not be applicable to a standard VGA implementation.
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Presented to roughly based upon their place in the graphics pipeline between
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the CPU and the video outputs are the:
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<UL>
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<LI>
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<A HREF="graphreg.htm">Graphics Registers</A> -- control the way the CPU
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accesses video RAM.</LI>
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<LI>
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<A HREF="seqreg.htm">Sequencer Registers</A> -- control how video data
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is sent to the DAC.</LI>
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<LI>
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<A HREF="attrreg.htm">Attribute Controller Registers</A> -- selects the
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16 color and 64 color palettes used for EGA/CGA compatibility.</LI>
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<LI>
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<A HREF="crtcreg.htm">CRT Controller Registers</A> -- control how the video
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is output to the display.</LI>
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<LI>
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<A HREF="colorreg.htm">Color Registers</A> -- selects the 256 color palette
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from the maximum possible colors.</LI>
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<LI>
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<A HREF="extreg.htm">External Registers</A> -- miscellaneous registers
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used to control video operation.</LI>
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</UL>
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<A NAME="index"></A><B>Indices</B>
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<BR> In order to locate a particular
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register quickly, the following indexes are provided. The first is a listing
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of all of the register fields of the VGA hardware. This is especially useful
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for fields that are split among multiple registers, or for finding the
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location of a field that are packed in with other fields in one register.
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The second is indexed by function groups each pertaining to a particular
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part of the VGA hardware. This makes understanding and programming the
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VGA hardware easier by listing the fields by subsystem, as the VGA's fields
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are grouped in a somewhat haphazard fashion. The third is intended for
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matching a read or write to a particular I/O port address to the section
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where it is described.
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<UL>
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<LI>
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<A HREF="vgargidx.htm">VGA Field Index</A> -- An alphabetical listing of
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all fields and links to their location.</LI>
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<LI>
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<A HREF="vgafunc.htm">VGA Functional Index</A> -- A listing of all fields
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and links to their location grouped by function.</LI>
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<LI>
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<A HREF="portidx.htm">VGA I/O Port Index</A> -- A listing of VGA I/O ports
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in numerical order.</LI>
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</UL>
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Notice: All trademarks used or referred to on this page are the property
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of their respective owners.
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<BR>All pages are Copyright © 1997, 1998, J. D. Neal, except where
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noted. Permission for utilization and distribution is subject to the terms
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of the <A HREF="license.htm">FreeVGA Project Copyright License</A>.
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<P>
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</BODY>
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</HTML>
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