HOW TO: US Robotics Modem Configuration in Linux

The following configuration applies to commonly used US Robotics modems:

1. Dip Switches

Sportster modems should be set initially for:

  • DIP switches 3,7, and 8 down (The rest UP)

Switch3 Down is display result codes

Switch7 Down is Load factory defaults

Switch8 Down is Smart Mode

Courier modems should be set initially for:

  • DIP switches 3 and 8 ON (The rest OFF)

Switch3 On Display Result Codes

Switch8 On Enable AT Command Set



# dinc 19200 /dev/ttyxyz


The at&b1 setting configures a fixed serial port rate on the modem.

3. The port should set for RTS and CTS flow control. In Linux this is command is:

This command can be placed in /etc/init.d/dgrp_ditty to keep the configuration over reboots.

4. If using 8-wire RJ45 cabling (non-Digi cabling), the altpin setting will need to be applied to the Digi unit.  Telnet to the Digi unit, login as root and issue the following command:

  • Switch 5 Up/Off is Auto Answer onfirst ring (or higher if specified in NVRAM with ATS0=# -- the default isS0=1). Thus ATS0 does not need to be set for most applications.
  • To verify DTE port speed on the modem, use the command:


  • Some 14.4+ Modems will not workreliably if set for speeds below 38400.
Last updated: Jun 23, 2019

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