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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968" /><title>Chapter 4. Port Space Accesses</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /><link rel="home" href="index.html" title="Bus-Independent Device Accesses" /><link rel="up" href="index.html" title="Bus-Independent Device Accesses" /><link rel="prev" href="ch03s02.html" title="Accessing the device" /><link rel="next" href="ch04s02.html" title="Accessing Port Space" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 4. Port Space Accesses</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch03s02.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="ch04s02.html">Next</a></td></tr></table><hr /></div><div class="chapter" title="Chapter 4. Port Space Accesses"><div class="titlepage"><div><div><h2 class="title"><a id="port_space_accesses"></a>Chapter 4. Port Space Accesses</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="ch04.html#port_space_explained">Port Space Explained</a></span></dt><dt><span class="sect1"><a href="ch04s02.html">Accessing Port Space</a></span></dt></dl></div><div class="sect1" title="Port Space Explained"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="port_space_explained"></a>Port Space Explained</h2></div></div></div><p>
Another form of IO commonly supported is Port Space. This is a
range of addresses separate to the normal memory address space.
Access to these addresses is generally not as fast as accesses
to the memory mapped addresses, and it also has a potentially
smaller address space.
</p><p>
Unlike memory mapped IO, no preparation is required
to access port space.
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