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Retidy, removing align=left from headings and empty paragraphs

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James Gregory 2013-12-30 15:37:13 +11:00
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@ -1,5 +1,4 @@
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
@ -19,17 +18,21 @@
<center>
<table border="1">
<tr>
<td><a href="26-03.html">Previous</a></td>
<td>
<a href="26-03.html">Previous</a>
</td>
<td><a href="index.html">Table of Contents</a></td>
<td>
<a href="index.html">Table of Contents</a>
</td>
<td><a href="27-02.html">Next</a></td>
<td>
<a href="27-02.html">Next</a>
</td>
</tr>
</table>
</center>
<p><br /></p>
<h2 id="Heading1">Chapter 27<br />
Yet Another VGA Write Mode</h2>
@ -51,7 +54,7 @@
<p>It&rsquo;s possible that you understand write mode 2 thoroughly at this point; nonetheless, I suspect that some additional explanation of an admittedly non-obvious mode wouldn&rsquo;t hurt. Let&rsquo;s follow the CPU byte through the VGA in write mode 2, step by step.</p>
<h4 align="left" id="Heading4">A Byte&rsquo;s Progress in Write Mode 2</h4>
<h4 id="Heading4">A Byte&rsquo;s Progress in Write Mode 2</h4>
<p>Figure 27.1 shows the write mode 2 data path. The CPU byte comes into the VGA and is split into four separate bits, one for each plane. Bits 7-4 of the CPU byte vanish into the bit bucket, never to be heard from again. Speculation long held that those 4 unused bits indicated that IBM would someday come out with an 8-plane adapter that supported 256 colors. When IBM did finally come out with a 256-color mode (mode 13H of the VGA), it turned out not to be planar at all, and the upper nibble of the CPU byte remains unused in write mode 2 to this day.</p>
@ -74,16 +77,20 @@
<p>Write mode 2 is selected by setting bits 1 and 0 of the Graphics Mode register (Graphics Controller register 5) to 1 and 0, respectively. Since VGA registers are readable, the correct way to select write mode 2 on the VGA is to read the Graphics Mode register, mask off bits 1 and 0, OR in 00000010b (02H), and write the result back to the Graphics Mode register, thereby leaving the other bits in the register undisturbed.</p>
<p><br /></p>
<center>
<table border="1">
<tr>
<td><a href="26-03.html">Previous</a></td>
<td>
<a href="26-03.html">Previous</a>
</td>
<td><a href="index.html">Table of Contents</a></td>
<td>
<a href="index.html">Table of Contents</a>
</td>
<td><a href="27-02.html">Next</a></td>
<td>
<a href="27-02.html">Next</a>
</td>
</tr>
</table>
</center>