Omega A2400 - Manual (Page 9)

Getting Started 1-5
values (NULL, CR, $, #, {, }). A dummy address must be included in every
command for proper responses.
Setup information in an A2400 may be changed at will with the SetUp (SU)
command. Baud rates and parity setups may be changed without affecting
the Default values of 300 baud and no parity. When the
DEFAULT* pin is released, the module automatically performs a program
reset and configures itself to the baud rate and parity stored in the setup
information.
The Default Mode is intended to be used with a single module connected to
a terminal or computer for the purpose of identifying and modifying setup
values. During normal operation, the DEFAULT* pin should be left open.