Ref: 13420012
Title: Configuring 3S/5xx Server Serial Ports for 3+Share
date: 5/4/90

Copyright 3Com Corporation, 1991.  All rights reserved.

Serial ports on 3Com's 3S/5xx dedicated servers using the 3+Share
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 supports data rates up to 19.2 kBd.  It conforms
to the EIA RS-232C specification and is wired as a DTE device.

COM2 and Localtalk:  These two ports originate from a Z8530 two-channel
synchronous device.  The A channel (COM2) is wired for normal RS-232
communications.  Port A supports synchronous and asynchronous communications
up to 19.2K baud.  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 COM2 be used for high speed devices (for example,
19.2 kBd modems).  For slower devices, either COM1 or COM2 can be used.
