4
AT COMMAND SET
Command Guidelines
The basic AT commands used to control modem operation are defined in this section. Under AT operation,
the modem performs autobaud, autoparity and autolength functions on each header entered. The autoparity
and autolength facilities can detect 7 or 8-bit characters of even, odd, or no parity with one stop bit.
Command Format
A command line is a string of characters sent from a DTE to the modem (DCE) while the modem is in a
command state. A command line has a prefix, a body, and a terminator. Each command line (with the
exception of the A/command) must begin with the character sequence AT and must be terminated by a
carriage return.
Characters within the command line are parsed as commands with associated parameter values. The basic
commands consist of single ASCII characters, or single characters preceded by a prefix character (e.g., "&"),
followed by a decimal parameter. Missing decimal parameters are evaluated as 0.
The AT sequence may be followed by any number o f commands in sequence, except for commands such as
Z, D, or A. Commands following commands Z, D, or A on the same command line will be ignored. The
maximum number of characters on any command line is 39 (including "A" and "T"). If a syntax error is found
anywhere in a command line command, the remainder of the line will be ignored and the ERROR result code
will be returned.
Escape Code Sequence
When the modem has established a connection and has entered on-line data mode, it is possible to break
into the data transmission in order to issue further commands to the modem in an on-line command mode.
This is achieved by sending to the modem a sequence of three ASCII characters specified by register S2.
The default character is '+'. The timing of the three characters must comply with specific time constraints.
There is a guard time before the first character (the pre-sequence time), a guard time following the third
character (the post-sequence time), and a guard time-out between the first and second characters and
between the second and third characters (the inter-character time). These times are controlled by the value
recorded in register S12.
Command Set Detail
The modem will respond to the commands detailed below. Parameters applicable to each command a re
listed with the command description. The defaults shown for each configuration command are those used in
factory profile 0.
AT COMMANDS
A/ - Re-execute Command
The modem behaves as though the last command line had been re-sent by the DTE. "A/" will repeat all the
commands in the command buffer.
AT=x - Write to Selected S-Register
This command writes the value x to the currently selected S-Register. An S-Register can be selected by
using the ATSn command.
