Here is what I wrote for myself about this issue on Debian Woody.
I have since moved over to Ubuntu and I thought that I updated some
instructions for myself. I just can't find them.<br>
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<a href="http://jrasmussen0.blogspot.com/2004/07/creating-serial-port-for-internal.html" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">http://jrasmussen0.blogspot.com/2004/07/creating-serial-port-for-internal.html
</a><br>
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Basically, you have to configure a /dev/ttyS[1-4] device that works as
a serial connection to the hardware address of your device.
Setserial is the software you need to configure this, however it is not
part of Ubuntu's default installation. You will need to download
the deb package and manually install it with 'dpkg -i' I can't
remember if there are any dependencies that have to be manually
installed at the same time.<br><br>-- <br>Jeff Rasmussen<br>GPG public key 0x9686C12F