82 lines
3.5 KiB
HTML
82 lines
3.5 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
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<!--Converted with LaTeX2HTML 96.1-c (Feb 29, 1996) by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds -->
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<HTML>
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<HEAD>
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<TITLE>Accessing Serial Devices</TITLE>
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</HEAD>
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<BODY LANG="EN">
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<A HREF="node1.html"><IMG WIDTH=65 HEIGHT=24 ALIGN=BOTTOM ALT="contents" SRC="contents_motif.gif"></A> <BR>
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<B> Next:</B> <A HREF="node57.html">Serial Hardware</A>
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<B>Up:</B> <A HREF="node53.html">Setting up the Serial </A>
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<B> Previous:</B> <A HREF="node55.html">Introduction to Serial Devices</A>
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<BR> <P>
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<H1><A NAME="SECTION006300000">Accessing Serial Devices</A></H1>
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<P>
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<A NAME="serialdevices"></A>
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Like all devices in a system, serial ports are accessed
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through device special files, located in the /dev directory.
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There are two varieties of device files related to serial drivers,
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and for each port, there is one device file from each of them.
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Depending on the file it is accessed by, the device will behave
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differently.
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<P>
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<A NAME="2396"></A>
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<A NAME="2397"></A>
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<A NAME="2322"></A>
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<A NAME="2323"></A>
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<A NAME="2324"></A>
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The first variety is used whenever the port is used for dialing in; it
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has a major number of-4, and the files are named ttyS0,
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ttyS1, etc. The second variety is used when dialing out
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through a port; the files are called cua0, etc, and
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have a major number of-5.
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<P>
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<A NAME="2328"></A>
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<A NAME="2329"></A>
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Minor numbers are identical for both types. If you have your modem on
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one of the ports COM1 through COM4, its minor number will
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be the COM port number plus 63. If your setup is different from
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that, for example when using a board supporting multiple serial lines,
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please refer to the Serial Howto.
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<P>
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Assume your modem is on COM2. Thus its minor number will be-65,
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and its major number will be 5 for dialing out. There should be a
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device cua1 which has these numbers. List the serial ttys in
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the /dev directory. Columns 5 and 6 should show major and minor
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numbers, respectively:
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<pre>
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$ ls -l /dev/cua*
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crw-rw-rw- 1 root root 5, 64 Nov 30 19:31 /dev/cua0
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crw-rw-rw- 1 root root 5, 65 Nov 30 22:08 /dev/cua1
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crw-rw-rw- 1 root root 5, 66 Oct 28 11:56 /dev/cua2
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crw-rw-rw- 1 root root 5, 67 Mar 19 1992 /dev/cua3
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</pre>
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If there is no such device, you will have to create one: become
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super-user and type
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<pre>
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# mknod -m 666 /dev/cua1 c 5 65
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# chown root.root /dev/cua1
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< /pre>
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Some people suggest making /dev/modem a symbolic link to your
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modem device, so that casual users don't have to remember the somewhat
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un-intuitive cua1. However, you cannot use modem in one
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program, and the real device file name in another. This is because
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these programs use so-called <em>lock files</em> to signal that the
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device is used. By convention, the lock file name for cua1, for
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instance, is LCK..cua1. Using different device files for the
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same port means that programs will fail to recognize each other's lock
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files, and will both use the device at the same time. As a result, both
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applications will not work at all.
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<P>
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<HR><A HREF="node1.html"><IMG WIDTH=65 HEIGHT=24 ALIGN=BOTTOM ALT="contents" SRC="contents_motif.gif"></A> <BR>
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<B> Next:</B> <A HREF="node57.html">Serial Hardware</A>
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<B>Up:</B> <A HREF="node53.html">Setting up the Serial </A>
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<B> Previous:</B> <A HREF="node55.html">Introduction to Serial Devices</A>
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<P><ADDRESS>
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<I>Andrew Anderson <BR>
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Thu Mar 7 23:22:06 EST 1996</I>
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</ADDRESS>
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</BODY>
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</HTML>
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