ABB 1MRS119000 Operator's Manual page 16

3.3.3
3.3.4
16
AT 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 charac-
ter sequence AT and must be terminated by a carriage return. Commands entered in upper
case or lower case are accepted, but both the A and T must be of the same case, i.e., "AT"
= ASCII 065, 084 or `at` = ASCII 097, 116. The body is a string of commands restricted
to printable ASCII characters (032 - 126). Space characters (ASCII 032) and control char-
acters other than CR (ASCII 013) and BS (ASCII 010) in the command string are ignored.
The default terminator is the ASCII <CR> character. Characters that precede the AT pre-
fix are ignored. The command line interpretation begins upon receipt of the carriage re-
turn character.
Characters within the command line are parsed as commands with associated parameter
values. The basic commands consist of single ASCII characters, or single characters pre-
ceded by a prefix character (e.g., `&"), followed by a decimal parameter. Missing decimal
parameters are evaluated as 0.
The modem supports the editing of command lines by recognizing a backspace character.
When modem echo is enabled, the modem responds to the receipt of a backspace or delete
by echoing a backspace character, a space character, and another backspace. The hex value
to be used for the backspace character is programmable through register S5. Values equal
to 0 or greater than 127, or the value which corresponds to the carriage return character,
cannot be used for the backspace character. This editing is not applicable to the AT header
of a command. A command line may be aborted at any time by entering < cntrl-x > (18h).
The AT sequence may be followed by any number of 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.
Most of the commands entered with parameters out of range will be rejected and the
ERROR response will be returned to the DTE.
Commands will be accepted by the modem once the previous command has been fully
executed This is normally indicated by the return of an appropriate result code. Execution
of commands D and A, either as a result of a direct command or a re-execute command,
will be aborted if another character is entered before completion of the handshake.
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 the DTE 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 sec-
ond characters and between the second and third characters (the inter-character time).
These times are controlled by the value recorded in register S12.