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+ <META NAME="Author" CONTENT="Joshua Neal">
+ <META NAME="Description" CONTENT="Pure VGA/SVGA hardware programming (registers, identification, and otherlow-level stuff.)">
+ <META NAME="KeyWords" CONTENT="VGA SVGA hardware video programming">
+ <TITLE>VGA/SVGA Video Programming--Manipulating the Text-mode Cursor</TITLE>
+</HEAD>
+<BODY>
+
+<CENTER><A HREF="../home.htm">Home</A> <A HREF="#intro">Intro</A> <A HREF="#enable">Visibility</A>
+<A HREF="#position">Position</A> <A HREF="#shape">Shape</A> <A HREF="#blink">Blink
+Rate</A> <A HREF="#color">Color</A> <A HREF="vga.htm#general">Back</A>
+<HR WIDTH="100%"><B>Hardware Level VGA and SVGA Video Programming Information
+Page</B></CENTER>
+
+<CENTER>Manipulating the Text-mode Cursor
+<HR WIDTH="100%"></CENTER>
+
+<UL>
+<LI>
+<A HREF="#intro">Introduction</A> -- gives overview of text-mode cursor
+capabilities</LI>
+
+<LI>
+<A HREF="#enable">Enabling/Disabling the Cursor</A> -- details on making
+the cursor visible or not visible</LI>
+
+<LI>
+<A HREF="#position">Manipulating the Cursor Position</A> -- details on
+controlling the cursor's placement</LI>
+
+<LI>
+<A HREF="#shape">Manipulating the Cursor Shape</A> -- details on controlling
+the cursor's appearance</LI>
+
+<LI>
+<A HREF="#blink">Cursor Blink Rate</A> -- provides information about the
+cursor's blink rate</LI>
+
+<LI>
+<A HREF="#color">Cursor Color</A> -- provides information regarding the
+cursor's color</LI>
+</UL>
+<A NAME="intro"></A><B>Introduction</B>
+<BR><B> </B>When dealing with
+the cursor in most high-level languages, the cursor is defined as the place
+where the next text output will appear on the display. When dealing directly
+with the display, the cursor is simply a blinking area of a particular
+character cell. A program may write text directly to the display independent
+of the current location of the cursor. The VGA provides facilities for
+specifying whether a cursor is to be displayed, where the cursor is to
+appear, and the shape of the cursor itself. Note that this cursor is only
+used in the text modes of the standard VGA and is not to be confused with
+the graphics cursor capabilities of particular SVGA chipsets.
+
+<P><A NAME="enable"></A><B>Enabling/Disabling the Cursor</B>
+<BR> On the VGA there are three
+main ways of disabling the cursor. The most straightforward is to set the
+<A HREF="crtcreg.htm#0A">Cursor Disable</A> field to 1. Another way is
+to set the <A HREF="crtcreg.htm#0B">Cursor Scan Line End</A> field to a
+value less than that of the <A HREF="crtcreg.htm#0A">Cursor Scan Line Start</A>
+field. On some adapters such as the IBM EGA, this will result instead in
+a split block cursor. The third way is to set the cursor location to a
+location off-screen. The first two methods are specific to VGA and compatible
+adapters and are not guaranteed to work on non-VGA adapters, while the
+third method should.
+
+<P><A NAME="position"></A><B>Manipulating the Cursor Position</B>
+<BR><B> </B>When dealing with
+the cursor in standard BIOS text modes, the cursor position is specified
+by row and column. The VGA hardware, due to its flexibility to display
+any different text modes, specifies cursor position as a 16-bit address.
+The upper byte of this address is specified by the <A HREF="crtcreg.htm#0E">Cursor
+Location High Register</A>, and the lower by the <A HREF="crtcreg.htm#0F">Cursor
+Location Low Register</A>. In addition this value is affected by the <A HREF="crtcreg.htm#0B">Cursor
+Skew</A> field. When the hardware fetches a character from display memory
+it compares the address of the character fetched to that of the cursor
+location added to the <A HREF="crtcreg.htm#0B">Cursor Skew</A> field. If
+they are equal and the cursor is enabled, then the character is written
+with the current cursor pattern superimposed. Note that the address compared
+to the cursor location is the address in display memory, not the address
+in host memory. Characters and their attributes are stored at the same
+address in display memory in different planes, and it is the odd/even addressing
+mode usually used in text modes that makes the interleaved character/attribute
+pairs in host memory possible. Note that it is possible to set the cursor
+location to an address not displayed, effectively disabling the cursor.
+<BR> The <A HREF="crtcreg.htm#0B">Cursor
+Skew</A> field was used on the EGA to synchronize the cursor with internal
+timing. On the VGA this is not necessary, and setting this field to any
+value other than 0 may result in undesired results. For example, on one
+particular card, setting the cursor position to the rightmost column and
+setting the skew to 1 made the cursor disappear entirely. On the same card,
+setting the cursor position to the leftmost column and setting the skew
+to 1 made an additional cursor appear above and to the left of the correct
+cursor. At any other position, setting the skew to 1 simply moved the cursor
+right one position. Other than these undesired effects, there is no function
+that this register can provide that could not be obtained by simply increasing
+the cursor location.
+
+<P><A NAME="shape"></A><B>Manipulating the Cursor Shape</B>
+<BR><B> </B> On the VGA, the text-mode
+cursor consists of a line or block of lines that extend horizontally across
+the entire scan line of a character cell. The first, topmost line is specified
+by the <A HREF="crtcreg.htm#0A">Cursor Scan Line Start</A> field. The last,
+bottom most line is specified by the <A HREF="crtcreg.htm#0B">Cursor Scan
+Line End</A> field. The scan lines in a character cell are numbered from
+0 up to the value of the <A HREF="crtcreg.htm#09">Maximum Scan Line</A>
+field. On the VGA if the <A HREF="crtcreg.htm#0B">Cursor Scan Line End</A>
+field is less than the <A HREF="crtcreg.htm#0A">Cursor Scan Line Start</A>
+field, no cursor will be displayed. Some adapters, such as the IBM EGA
+may display a split-block cursor instead.
+
+<P><A NAME="blink"></A><B>Cursor Blink Rate</B>
+<BR> On the standard VGA, the
+blink rate is dependent on the vertical frame rate. The on/off state of
+the cursor changes every 16 vertical frames, which amounts to 1.875 blinks
+per second at 60 vertical frames per second. The cursor blink rate is thus
+fixed and cannot be software controlled on the standard VGA. Some SVGA
+chipsets provide non-standard means for changing the blink rate of the
+text-mode cursor.
+
+<P><A NAME="color"></A><B>Cursor Color</B>
+<BR> On the standard VGA, the
+cursor color is obtained from the foreground color of the character that
+the cursor is superimposing. On the standard VGA there is no way to modify
+this behavior.
+<BR>
+
+<P>Notice: All trademarks used or referred to on this page are the property
+of their respective owners.
+<BR>All pages are Copyright © 1997, 1998, J. D. Neal, except where
+noted. Permission for utilization and distribution is subject to the terms
+of the <A HREF="license.htm">FreeVGA Project Copyright License</A>.
+<BR>
+</BODY>
+</HTML>
projects / pintos-anon / blobdiff