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61203153L2-20 Express 3000 User Manual A-1
Appendix A
AT Commands and
S-Registers
AT COMMANDS
AT commands issue directions to the Express 3000 via a VT-100 termi-
nal emulation session. The DTE serial port accepts AT commands only
when no calls are established; i.e., the carrier detect (CD) signal is in-
active. When a call is established, the CD signal is active and the port
is used for data. The port cannot be used simultaneously to issue AT
commands and transmit and receive data. After entering command
mode (CD inactive), you can transmit AT commands to the Express
3000 to configure most options, dial remote Express 3000s, and initiate
tests to check both the Express 3000 and the network connections.
Escape Sequence and Guard Time Delay
To exit data mode (CD active) and enter command mode, the DTE se-
rial port must transmit a proper escape sequence to the Express 3000.
A specified time delay must occur between the last data character and
the first escape sequence character. This delay is the guard time delay.
You can change the guard time by writing a value to the S12 register.
For a valid escape sequence to occur, the DTE must transmit the es-
cape code character
three
times in succession with the delay between
each character less than the guard time.
The default escape sequence is
+++
and the default guard time delay
is one second.