23. Writing SMS Messages to Memory / Message Storage (AT+CMGW)

The AT command +CMGW (command name in text: Write Message to Memory) is used to write an SMS message to memory (i.e. message storage). The memory/message storage area to which SMS messages are written is specified by the +CPMS AT command (command line in text: Preferred Message Storage). Details about the +CPMS AT command can be found in the earlier section "Preferred Message Storage (AT+CPMS)" of this SMS tutorial.


23.1. Syntax of the +CMGW AT Command in SMS Text Mode

In SMS text mode, the syntax of the +CMGW AT command is: (Optional parameters are enclosed in square brackets.)


+CMGW[=address[,address_type[,message_status]]]<CR>sms_message_body<Ctrl+z>


Before we discuss each of the parameters, let's see an example that gives you some idea of how an actual command line should look like:


AT+CMGW="+85291234567",145,"STO UNSENT"<CR>This is an example for illustrating the syntax of the +CMGW AT command in SMS text mode.<Ctrl+z>


The address Parameter

The first parameter of the +CMGW AT command, address, specifies the destination address to send the SMS message to. Usually it is a mobile number formatted using the typical ISDN / telephony numbering plan (ITU E.164/E.163). For example, "+85291234567" and "91234567". Note that the value passed to the address parameter should be a string, i.e. it should be enclosed in double quotes.

The address parameter is optional and so it can be omitted. Later when you want to send the SMS message out, you can specify the destination address by the +CMSS AT command (command name in text: Send Message from Storage).


The address_type Parameter

The second parameter of the +CMGW AT command, address_type, specifies the type of the address assigned to the address parameter. Two values are commonly used. They are 129 and 145:

As address_type is an optional parameter, it can be omitted. If you do so, the GSM/GPRS modem or mobile phone will use the default value of the address_type parameter, which is:


The message_status Parameter

The third parameter of the +CMGW AT command, message_status, specifies the status of the SMS message to be written. The SMS specification has defined four status values:

Note that the value assigned to the message_status parameter should be a string. Thus, it should be enclosed in double quotes.

As message_status is an optional parameter, it can be omitted. If you do so, the GSM/GPRS modem or mobile phone will use the default value of the message_status parameter, which is "STO UNSENT".


The <CR> Character

<CR>, which represents the carriage return character, follows the message_status parameter. When the GSM/GPRS modem or mobile phone receives the carriage return character, it will send back a prompt formed by these four characters: the carriage return character, the linefeed character, the ">" character and the space character. If you don't understand what this means, don't worry. This should be clear to you when you see the example in the section "Example Demonstrating How to Use the +CMGW AT Command to Write SMS Text Messages to Message Storage in SMS Text Mode".


The sms_message_body Parameter

The fourth parameter of the +CMGW AT command, sms_message_body, specifies the SMS message body to be written to the memory/message storage area. Entering the <Esc> character will cancel the +CMGW AT command. If you don't understand what this means, see the example in the section "Example Demonstrating How to Use the +CMGW AT Command to Write SMS Text Messages to Message Storage in SMS Text Mode".


The <Ctrl+z> Character

When you finish entering the SMS message body, you have to enter the <Ctrl+z> character to mark the end of the SMS message body. The GSM/GPRS modem or mobile phone will then attempt to write the SMS message to the memory/message storage area.


23.2. SMSC Number Stored with the SMS Message (SMS Text Mode)

In SMS text mode, the +CMGW AT command does not have a parameter that allows you to specify an SMSC number. (Note that the +CMGW AT command does have such parameter when the GSM/GPRS modem or mobile phone is operating in SMS PDU mode.) However, when an SMS message is written to message storage, an SMSC number is actually stored with it. The SMSC number stored is the one specified by the +CSCA AT command (command name in text: Service Centre Address). Later if you send the SMS message, it will be transmitted through this SMSC. Once an SMS message has been written to message storage, it is not possible to change the SMSC number stored with the SMS message by using AT commands.

Note that it is possible that the command behavior on your mobile device is slightly different from what was described above.

More information about this issue is available in the "SMSC Number to be Used by the +CMSS AT Command to Send SMS Messages" section of this SMS tutorial.


23.3. Format of the Information Response of the +CMGW AT Command in SMS Text Mode

If the GSM/GPRS modem or mobile phone writes the SMS message to the message storage area successfully, it will return an information response to the computer / PC. In SMS text mode, the information response of the +CMGW AT command has the following format:


+CMGW: index


index is an integer that tells us the memory location to which the SMS message was written in the message storage area.


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