Ref: 10710035
Title: Appletalk and the COM5 Port
Date:  7/5/88

Copyright 3Com Corporation, 1991.  All rights reserved.

COM5 and the AppleTalk port are one and the same port.  Only one
or the other function can be selected at any given time.

Q:  Since Serial port number 5 is the same as the AppleTalk, and
port 4 and 5 share some architecture, is there any problem with
using com4?

A:  Yes, there would be some performance penalty.

Whenever the server gets a serial interrupt from COM4, it must
abort any current DMA transmit or receive that is currently
active on the AppleTalk port in order to service the interrupt.
At 9600 baud this makes the problem quite apparent.

The result is slow AppleTalk throughput, so if the server is
receiving spooled information, you would notice slow print performance.

Try to avoid using COM4 if you can when AppleTalk is configured.
