3Com 56k User's Manual And Reference page 26

Follow the on-screen instructions to access the
COM port settings panel. In this panel you should
find the UART chip used. Match the UART type
listed in MSD with the serial rate listed in the
chart. Select this serial rate in any fax/data
programs you use.
If this is your UART...
16550
16450
8250
Do not select a 28,800, 14,400, or 12,000 bps serial
port rate if offered. Your modem will not work
correctly with any of these settings. Fix or lock the
serial port (baud) rate. If it's referred to as
autobaud, select OFF.
Congratulations!
You are now ready to start using your
3Com U.S. Robotics 56K Faxmodem
22
Software Installation
Select this serial rate
115.2 or 57.6 Kbps
38.4 Kbps
19.2 Kbps