Westermo TF-300 - Manual (Page 10)

10 6606-2201
DTE Command lines
A command line is a string of characters send 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 must begin with the character sequence AT and must be terminated by a car-
riage 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., ÓATÓ (ASCII 065, 084) or ÓatÓ = (ASCII 097, 116).
The body is a string of commands restricted to printable ASCII characters (032-126).
Space characters (ASCII 032) and control characters other than CR (ASCII 013) and BS
(ASCII 008) in the command string are ignored. The default terminator is the CR (ASCII
013) character. Characters that precede the AT prefix are ignored. The command line
interpretation begins upon receipt of the carriage return 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., Ô&Õ or Ô%Õ), followed by a decimal parameter.
The modem supports the editing of command lines by recognizing a backspace or delay
character. When modem echo is enabled, the modem responds to receipt of a backspace or
delete by echoing a backspace character, a space character, and another backspace. A com-
mand line may be aborted at anytime by entering < ctrl-x > (ASCII 024).
The AT sequence may be followed by any number of commands in sequence, except for
commands such as Z, D, O or H. Commands following Z, D, O or H on the same com-
mand 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 com-
mand, the remainder of the line will be ignored and the ERROR result code will be
returned to the DTE.
Commands entered with parameters out of range will not be accepted and the ERROR
result code will be returned to the DTE. Commands will only be accepted by the modem
once the previous command has been fully executed, which is normally indicated by the
return of an appropriate result code. Execution of command D will be aborted if another
characters is received from DTE before completion of the handshake.
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 and a guard time following the third character and
also between each character. This guard-time is set to one second in all cases. If other
characters are received within the guard time the escape sequence is not recognized.