Ref: 13420011
Title: Configuring 3S/5xx Server Serial Ports for 3+Open
date: 5/4/90

Copyright 3Com Corporation, 1991.  All rights reserved.

Serial ports on 3Com's 3S/5xx dedicated servers using the 3+Open network
operating system are wired and configured as follows:

COM1:  Normal AT-type asynchronous serial port using port I/O address
of 3F8 and IRQ 4.  It is implemented with a 16C450 UART (Universal
Asynchronous Receiver/Transmitter) and it supports data rates up to
19.2 kBd.  It conforms to the EIA RS-232C specification and is
wired as a DTE device.

COM3 and Localtalk:  These two ports originate from a Z8530
two channel synchronous device.  The A channel (COM3) is
wired for normal RS-232 communications.  Port A supports
synchronous and asynchronous communications up to 19.2 kBd.
The B channel (Localtalk) is implemented with RS-422 line drivers
and receivers.  Both ports share IRQ 15 and due to software and hardware
compatibility issues, these ports cannot be used simultaneously.

It is recommended that COM3 be used for high speed devices (for example,
19.2 kBd modems).  For slower devices, either COM1 or COM3 can
be used.
