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2. SYNTAX AND PROCEDURES
The command and response syntax and procedures generally conform to referenced
recommendations and standards.
Since these recommendations and standards describe characteristics universal to a
large installed base of modems to a maximum degree, there may be syntax and
procedural differences due to extensions and behavioral differences in implemented
commands, parameters, and responses beyond that described in these
recommendations and standards.
The syntax and procedures described in this section are based on V.25ter with
additional information included for implemented extensions and behavioral differences
beyond V.25ter.
2.1 Alphabet
T
he T.50 International Alphabet 5 (IA5) is used in this document. Only the low-order
seven bits of each character are significant to the modem; any eighth or higher-order
bit(s), if present, are ignored for the purpose of identifying commands and parameters.
Lower-case characters are considered identical to their upper-case equivalents when
received by the modem from the DTE. Result codes from the modem are in upper case.
2.2 DTE Commands Lines
Words enclosed in <angle brackets> are references to syntactical elements. The
brackets are not used when the words appear in a command line, the brackets are not
used. Words enclosed in [square brackets] represent optional items which may be
omitted from the command line at the specified point. The square brackets are not used
when the words appear in the command line. Other characters that appear in syntax
descriptions must as included as shown.
Any modem responses are mentioned in terms of their alphabetic format; the actual
response issued will depend on the setting of parameters that affect response formats,
e.g., Q and V commands (see 2.7).
2.2.1 Command Line General Format
A
command line is made up of three elements: the prefix, the body, and the termination
character.
The command line prefix consists of the characters "AT" or "at" or, to repeat the
execution of the previous command line, the characters "A/" or "a/".
The body is made up of individual commands described in this document. Space
characters (IA5 2/0) are ignored and may be used freely 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.
The termination character may be selected by a user option (parameter S3), the default
being CR.
2.2.2 Command Line Editing
The character defined by parameter S5 (default, BS) is interpreted as a request from the
DTE to the modem to delete the previous character. Any control characters (IA5 0/0
through 1/15, inclusive) that remain in the command line after receipt of the termination
character are ignored by the modem.
The modem checks characters from the DTE first to see if they match the termination
character (S3), then the editing character (S5), before checking for other characters.
This ensures that these characters will be properly recognized even if they are set to