25.7. Example
Demonstrating How to Use the +CMGS AT Command to Send SMS Text
Messages in SMS PDU Mode
Now
let's see a more detailed example that demonstrates how to use the
+CMGS AT command to send SMS text messages in SMS PDU mode and how
the +CMGS AT command should be used together with other AT commands.
Instructing
the GSM/GPRS Modem or Mobile Phone to Operate in SMS PDU Mode
First,
instruct the GSM/GPRS modem or mobile phone to operate in SMS PDU
mode by entering the command line "AT+CMGF=0" in a terminal
program (for example, HyperTerminal in Microsoft Windows). Below
shows the response returned from Nokia 6021 to HyperTerminal after
the execution of the command line "AT+CMGF=0":
AT+CMGF=0 OK
The
final result code OK indicates the +CMGF AT command was executed
successfully. If the final result code ERROR is returned, it is
likely that the GSM/GPRS modem or mobile phone does not support SMS
PDU mode. To check whether the GSM/GPRS modem or mobile phone
supports SMS PDU mode, enter the command line "AT+CMGF=?"
in the terminal program. Here is the response returned from Nokia
6021 to HyperTerminal:
AT+CMGF=? +CMGF:
(0,1)
OK
The
values in the parentheses indicate the modes that the GSM/GPRS modem
or mobile phone can operate in. The value 0 represents SMS PDU mode
and the value 1 represents SMS text mode. From the above response, we
know that Nokia 6021 can operate in either SMS PDU mode or SMS text
mode. See the section titled "Selecting
the Operating Mode (AT+CMGF)" of this SMS tutorial if you
want to learn further details about the +CMGF AT command.
(Optional
in SMS PDU Mode) Setting the SMSC Number to be Used to Send SMS Text
Messages
Second,
set the SMSC number to be used to send SMS text messages by the AT
command +CSCA (command name in text: Service Centre Address). Usually
the default setting is correct and you do not need to make any
changes. In SMS PDU mode, you can skip this step since you can pass
the SMSC number to the +CMGS AT command as a parameter. This is
different from SMS text mode, in which the only way to set the SMSC
number for sending SMS text messages is by using the +CSCA AT
command.
Below
demonstrates how to use the +CSCA AT command to set "+85290000000"
as the SMSC number:
AT+CSCA="+85290000000" OK
Detailed
information about the +CSCA AT command can be found in the "Setting
or Reading the Service Center Address / SMSC Address (AT+CSCA)"
section of this SMS tutorial.
Sending
Text Messages
Third,
use the +CMGS AT command to send a text message to the SMSC. Suppose
you want to send the text message "It is easy to send text
messages." to the mobile phone number +85291234567 through the
SMS center at +85290000000, the hexadecimal sequence to be passed to
the +CMGS AT command should be:
07915892000000F001000B915892214365F7000021493A283D0795C3F33C88FE06CDCB6E32885EC6D341EDF27C1E3E97E72E
and
the length of the SMS-SUBMIT TPDU embedded in the hexadecimal
sequence is 42 octets. We have discussed how to obtain these values
in previous sections and so we will not talk about them again here.
Now
pass the length of the SMS-SUBMIT TPDU to the +CMGS AT command by
entering the following command line in a terminal program:
AT+CMGS=42
Then,
press the Enter key of the keyboard to send a carriage return
character to the GSM/GPRS modem or mobile phone. The GSM/GPRS modem
or mobile phone will send back a prompt
formed by four characters. They are the carriage return character,
the linefeed character, the ">" character and the space
character. If all characters are to be displayed, the
characters you have sent to and received from the GSM/GPRS modem or
mobile phone so far are:
AT+CMGS=42<CR> <CR><LF>><Space>
However,
the carriage return character and linefeed character have special
meanings to a terminal program. When a terminal program 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. So, here is what you
will actually see in a terminal program such as HyperTerminal:
AT+CMGS=42 >
If
you want to cancel the send command at this point, press the Esc key
on the keyboard. The GSM/GPRS modem or mobile phone will then return
the OK final result code. Here shows the response returned from Nokia
6021 (or Sony Ericsson T68i):
AT+CMGS=42 > OK
Some
mobile devices return a slightly different response. One example is
Philips 598:
AT+CMGS=42 >
OK
If
you do not want to cancel the send command, enter the hexadecimal
sequence containing the SMS text message that you want to send from
your computer / PC. When finished, press Ctrl+z on the keyboard. The
GSM/GPRS modem or mobile phone then attempts to send the SMS text
message to the SMSC and returns a response to the computer / PC.
Below shows what you should see in a terminal program:
AT+CMGS=42 >
07915892000000F001000B915892214365F7000021493A283D0795C3F33C88FE06CDCB6E32885EC6D341EDF27C1E3E97E72E +CMGS:
12
OK
The
value in the information response, 12, is the message reference
number allocated to the SMS text message by the GSM/GPRS modem or
mobile phone. The final result code OK indicates the sending of the
SMS text message was successful. If the execution of the +CMGS AT
command fails, the GSM/GPRS modem or mobile phone will return either
the final result code ERROR or +CMS ERROR.
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