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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="23-05.html">Previous</a></td>
<td>
<a href="23-05.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="24-01.html">Next</a></td>
<td>
<a href="24-01.html">Next</a>
</td>
</tr>
</table>
</center>
<p><br /></p>
<p>One possible solution to this problem is to pick a second page start address that has a 0 value for the lower byte, so only the Start Address High register ever needs to be set, but in the sample program in Listing 23.1 I&rsquo;ve gone for generality and always set both bytes. To avoid mismatched start address bytes, the sample program waits for pixel data to be displayed, as indicated by the Display Enable status; this tells us we&rsquo;re somewhere in the displayed portion of the frame, far enough away from vertical sync so we can be sure the new start address will get used at the next vertical sync. Once the Display Enable status is observed, the program sets the new start address, waits for vertical sync to happen, sets the new pel panning state, and then continues drawing. Don&rsquo;t worry about the details right now; page flipping will come up again, at considerably greater length, in later chapters.</p>
<table width="100%">
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<p>Now that we know what the VGA looks like in broad strokes and have a sense of what VGA programming is like, we can start looking at specific areas in depth. In the next chapter, we&rsquo;ll take a look at the hardware assistance the VGA provides the CPU during display memory access. There are four latches and four ALUs in those chips, along with some useful masks and comparators, and it&rsquo;s that hardware that&rsquo;s the difference between sluggish performance and making the VGA get up and dance.</p>
<p><br /></p>
<center>
<table border="1">
<tr>
<td><a href="23-05.html">Previous</a></td>
<td>
<a href="23-05.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="24-01.html">Next</a></td>
<td>
<a href="24-01.html">Next</a>
</td>
</tr>
</table>
</center>