15. General Syntax
of Extended AT Commands
The
general syntax of extended AT commands is straightforward. The syntax
rules are provided below. The syntax of basic AT commands is slightly
different. We will not cover the syntax of basic AT commands in this
SMS tutorial since all SMS messaging commands are extended AT
commands.
Syntax
rule 1. All command lines must start with "AT" and end
with a carriage return character. (We will use <CR> to
represent a carriage return character in this SMS tutorial.) In a
terminal program like HyperTerminal of Microsoft Windows, you can
press the Enter key on the keyboard to output a carriage return
character.
Example:
To list all unread inbound SMS messages stored in the message storage
area, type "AT", then the extended AT command "+CMGL",
and finally a carriage return character, like this:
AT+CMGL<CR>
Syntax
rule 2. A command line can contain more than one AT command. Only
the first AT command should be prefixed with "AT". AT
commands in the same command-line string should be separated with
semicolons.
Example:
To list all unread inbound SMS messages stored in the message storage
area and obtain the manufacturer name of the mobile device, type
"AT", then the extended AT command "+CMGL",
followed by a semicolon and the next extended AT command "+CGMI":
AT+CMGL;+CGMI<CR>
An
error will occur if both AT commands are prefixed with "AT",
like this:
AT+CMGL;AT+CGMI<CR>
Syntax
rule 3. A string is enclosed between double quotes.
Example:
To read all SMS messages from message storage in SMS text mode (at
this time you do not need to know what SMS text mode is. More
information will be provided later in this SMS tutorial), you need to
assign the string "ALL" to the extended AT command +CMGL,
like this:
AT+CMGL="ALL"<CR>
Syntax
rule 4. Information responses and result
codes (including both final result codes and unsolicited result
codes) always start and end with a carriage return character and a
linefeed character.
Example:
After sending the command line "AT+CGMI<CR>"
to the mobile device, the mobile device should return a response
similar to this:
<CR><LF>Nokia<CR><LF> <CR><LF>OK<CR><LF>
The
first line is the information response of the AT command +CGMI and
the second line is the final result code. <CR>
and <LF>
represent a carriage return character and a linefeed character
respectively. The final result code "OK" marks the
end of the response. It indicates no more data will be sent from the
mobile device to the computer / PC.
When
a terminal program such as HyperTerminal of Microsoft Windows sees a
carriage return character, it moves the cursor to the beginning of
the current line. When it sees a linefeed character, it moves the
cursor to the same position on the next line. Hence, the command line
"AT+CGMI<CR>"
that you entered and the corresponding response will be displayed
like this in a terminal program such as HyperTerminal of Microsoft
Windows:
AT+CGMI Nokia
OK
15.1. Information
Response and Final Result Code
Don't
forget the meanings of information response and final result code
stated above, since you will see these two terms frequently as you go
through this SMS tutorial.
AT+CGMI <--
Command line entered Nokia <-- Information response
OK <--
Final result code
15.2. Case
Sensitivity of AT Commands
In
the SMS specification, all AT commands are in uppercase letters.
However, many GSM/GPRS modems and mobile phones allow you to type AT
commands in either uppercase or lowercase letters. For example, on
Nokia 6021, AT commands are case-insensitive and the following two
command lines are equivalent:
AT+CMGL<CR>
at+cmgl<CR>
Feedback Form (ExpandCollapse)
|
|