Appendix B. At Commands - ADTRAN Async-232 User Manual

Appendix B
OVERVIEW
Configuring an Async-232 Module port for AT commands enables in-band call
dialing and answering over the DTE interface using asynchronous AT commands.
AT commands can be used to configure the port as well as establish and end a
call. AT commands and response messages may be separately enabled for incom-
ing and outgoing calls. For incoming calls, set the In Call Control field to AT
Cmds. For outgoing calls, set the Dialout Method field to AT Dial. Either option
or both must be enabled to issue AT commands to the port.
USING AT COMMANDS
Before a call is established or answered, the port accepts AT commands for config-
uration, status reporting, and dialing. After a call is established or answered and
the Data Carrier Detect (DCD) signal is driven active, the port enters data mode.
To exit data mode and enter command mode, the DTE must transmit a proper
escape sequence to the Async-232 Module port. A specified minimum time delay
must occur between the last data character and the first escape sequence character
as well as the last escape character and the next data character to enter command
mode. This is the guard time delay, and it can be changed by writing a value to
the S12 register. The default value for the guard time is one second. For a valid
escape sequence 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 +++. The escape character may be changed
or escape to command mode disabled using the S2 register. Recognition of escape
to command mode is automatically disabled if AT command mode is not enabled.
Once command mode is entered, AT commands can be transmitted to the port to
configure options, check device status, or hang-up the call with the ATH com-
mand. To return online to data-mode from command mode, enter ATO. All com-
mand lines must begin with the AT characters in capital or lower case letters and
end with a carriage return (ASCII decimal 13.) Before the terminating character is
transmitted, the command line can be edited by using the backspace character
61200182L1-1
If the Async-232 Module port is connected to a DTE that echoes all received charac-
ters, perhaps as part of a text menu interface, it may be useful to change the escape
character or turn it off to prevent entering command mode based on an escape sequence
received from a remote modem.
Async-232 Module User Manual
AT Commands
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