Rockwell RCV144ACx, Command Reference Manual

Page: 19 / 186

AT Command Reference Manual
1048 3-1
3. AT COMMAND SET
3.1 AT COMMAND GUIDELINES
The basic AT commands used to control modem operation are defined in this section. These commands are summarized in
Appendix A. All these commands may not be available in a specific product depending upon supported data rates and
modes. The default values are typical of a fully configured modem supporting all data rates and options. The actual default
value is dependent upon modem firmware as defined by the firmware release notes.
3.1.1 AT Commands, DTE Adaption
Under AT operation, the serial interfaced modem performs an autobaud/autoparity/autolength function on each AT header
entered. The autolength/autoparity facility can detect 7- or 8-bit characters of even, odd, or no parity with one stop bit. This is
not necessary for the parallel interfaced modem since it has direct access to the UART registers.
3.1.2 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 character 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 characters 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 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 preceded 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 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 commands entered with parameters out of range will not be accepted and the ERROR response 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 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.
3.1.3 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
maximum time allowed between receipt of the last character of the three escape character sequence from the DTE and
sending of the OK result code to the DTE is controlled by the S12 register.