Getting Started 2 - 39
Basic AT Command Syntax
A command line is made up of three elements:
•
Prefix - consists of the characters “AT” or “at” or, to repeat the execution of the previous command line, “A/”
or “a/”.
•
Body - made up of individual commands described later. Space characters (IA5 2/0) are ignored and may be
used for formatting purposes, unless they are embedded in numeric or string constants. The termination
character may not appear in the body. The modem can accept at least 40 characters in the body.
•
Termination character - may be selected by a user option (parameter S3). The default is CR.
The format of Basic Syntax commands, except for the D and S commands, is as follows:
<command>[<number>]
where:
•
<command> is either a single character, or the “&” character followed by a single character per V.250; or the
“%” character followed by a single character, the “*” character followed by a single character, or the “^”
character followed by a single character.
•
<number> is a string of one or more characters from “0” through “9” representing a decimal integer value.
Commands expecting a <number> are noted in the description of the command. If <number> is missing from
such a command (<command> is immediately followed by another <command> or the termination
character), the value “0” is assumed. If a command does not expect a <number> and a number is present, an
error occurs. All leading “0”s in <number> are ignored by the modem.
Additional commands may follow a command (and associated parameter, if any) on the same command line with a
separation character. The actions of some commands cause the rest of the command line to be ignored.
S-Parameters
Commands that begin with the letter “S” are known as “S-parameters”. The number following the “S” indicates the
“parameter number” referenced. If the number is not recognized as a valid parameter number, an ERROR result
code issues. Immediately following this number, either a “?” or “=” character must appear. “?” is used to read the
current value of the indicated S-parameter; “=” sets the S-parameter to a new value.
S<parameter_number>?
S<parameter_number>=[<value>]
If the “=” is used, the new value to be stored in the S-parameter is specified in decimal following the “=”. If no value
is given (i.e., the end of the command line occurs or the next command follows immediately), the S-parameter
specified may be set to 0, or an ERROR result code issues and the stored value remains. The ranges of
acceptable values are given in the description of each S-parameter.
If the “?” is used, the modem transmits a single line of information text to the DTE. The text portion of this
information text consists of exactly three characters, giving the value of the S-parameter in decimal, with leading
zeroes included.
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