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61202.153L3-1 Express XRT User Guide 57
Appendix A
AT Commands and S-Registers
AT COMMANDS
While a call is not established, the DTE port accepts AT com-
mands. During this time, the CD signal is inactive. When a call is
established, the port is used for data. This data mode is indicated
by the CD signal active. The Express XRT can be configured and
controlled with AT commands from a serial port similarly to ana-
log modems.
To exit data mode and enter command mode, the serial port must
transmit a proper escape sequence to the Express XRT. A speci-
fied time delay must occur between the last data character and the
first escape sequence character. This is the guard time delay, and
it can be changed by writing a value to the S12 register. The de-
fault value for the guard time is one second. For a valid escape se-
quence to occur, the DTE must transmit the escape code character
three times in succession with delay between each character being
less than the guard time. The default escape sequence is +++.
Once command mode is entered, AT commands can be transmit-
ted to the Express XRT to configure most of the options, dial re-
mote Express XRTs, or initiate tests to check both the Express XRT
and the network connections. All command lines must begin with
the AT character set in either capital or lower case letters. To re-
turn an active call to the on-line state type ATO.
The command line may contain a single command or a series of
commands after the AT attention code. AT commands _L1 and
_L0 are exceptions and must be on a separate line followed by En-
ter. When a series of commands is used, the individual com-
mands may be separated with spaces for readability. The