26.3.8. Example Demonstrating How to Use the +CMGL AT Command to List SMS Text Messages from a Message Storage Area (SMS PDU Mode)
Now let's see a more detailed example that demonstrates how to use the +CMGL AT command to list SMS text messages from a message storage area when SMS PDU mode is used, and how the +CMGL 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":
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:
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.
Selecting the Message Storage Area to Read SMS Text Messages from
Second, use the AT command +CPMS (command name in text: Preferred Message Storage) to select the message storage area to read SMS text messages from. For example, to instruct the GSM/GPRS modem or mobile phone to use the message storage area in the SIM card for the AT command +CMGL, enter the command line 'AT+CPMS="SM"' in the terminal program. Then press the Enter key on the keyboard and you should see something similar to this:
Detailed information about the +CPMS AT command is available in the "Preferred Message Storage (AT+CPMS)" section of this SMS tutorial.
Listing SMS Text Messages
Third, use the +CMGL AT command to list SMS text messages from the message storage area. Suppose you would like to retrieve all new SMS messages received. As the status of new inbound SMS messages is "received unread", you should specify 0 to the +CMGL AT command, as shown below:
Since 0 is the default parameter value, you can simply omit it, like this:
Now press the Enter key on the keyboard and the GSM/GPRS modem or mobile phone will execute the command line "AT+CMGL". If successful, it returns all messages that have the "received unread" status in the message storage area. In a terminal program such as HyperTerminal of Microsoft Windows, the result should look something like this:
From above, we know that the message storage area contains two new inbound SMS text messages. Let's take the first SMS text message as an example to illustrate the meaning of different field values in the +CMGL information response above:
The value of the first field, 2, tells us the text message is stored in the memory location at index 2.
The value of the second field, 0, indicates the status of the text message is "received unread".
The value of the third field should be a string that contains the text associated to the sender's phone number "+85291234567" in the phonebook. In this example, this field is empty. One possible reason is that the GSM/GPRS modem or mobile phone (for example, Nokia 6021 and many other Nokia products) does not support this field.
The value of the fourth field, 51, tells us the TPDU encoded in the hexadecimal sequence consists of 51 octets.
The details of the SMS text message are encoded in the hexadecimal sequence. Examples include the sender's phone number, the body of the SMS text message, the time and date at which the SMS text message arrived at the SMS center, etc. We have discussed how to decode the hexadecimal sequence of an inbound SMS text message in the section titled "Some Explanation about the Decoding of the SMSC_number_and_TPDU Field Value of the +CMGR AT Command" of this SMS tutorial. Thus, we will not talk about it again here.
For the decoding of the hexadecimal sequence of an outgoing SMS text message, please refer to the "Some Explanation about the Coding of the SMSC_number_and_TPDU Parameter Value of the +CMGS AT Command" section of this SMS tutorial.
The final result code OK informs us that the SMS text messages were read from message storage successfully. If the execution of the +CMGL AT command fails, the GSM/GPRS modem or mobile phone will return either the final result code ERROR or +CMS ERROR.
After using the +CMGL AT command to list the SMS text messages, their status was changed from "received unread" to "received read". So, if the command line "AT+CMGL" is executed again, no text message will be returned. Here shows the response returned from Philips 598:
The response returned from Nokia 6021 is slightly different, as shown below. There seems to be a minor bug in Nokia's implementation. Two extra characters <CR><LF> are outputted and this does not follow the general syntax of extended AT commands.
To see the two text messages again, specify either 1 or 4 to the +CMGL AT command. The value 1 instructs +CMGL to list all messages that have the "received read" status from message storage, while the value 4 instructs +CMGL to list all messages from message storage. The response returned from the GSM/GPRS modem or mobile phone is slightly different from the earlier one. The changes are highlighted in bold type below:
|Previous Page||Page 65 of 65|
- 1. Introduction to SMS Messaging
- 2. What Makes SMS Messaging So Successful Worldwide?
- 3. Example Applications of SMS Messaging
- 4. What is an SMS Center / SMSC?
- 5. Basic Concepts of SMS Technology
- 6. Intra-operator SMS Messages
- 7. Inter-operator SMS Messages
- 8. International SMS Messages
- 9. What is an SMS Gateway?
- 10. How to Send SMS Messages from a Computer / PC?
- 11. How to Receive SMS Messages Using a Computer / PC?
- 12. Introduction to GSM / GPRS Wireless Modems
- 13. How to Use Microsoft HyperTerminal to Send AT Commands to a Mobile Phone or GSM/GPRS Modem?
- 14. Introduction to AT Commands
- 15. General Syntax of Extended AT Commands
- 16. Result Codes of AT Commands
- 17. AT Command Operations: Test, Set, Read and Execution
- 18. Testing the Communication between the PC and GSM/GPRS Modem or Mobile Phone
- 19. Checking if the GSM/GPRS Modem or Mobile Phone Supports the Use of AT Commands to Send, Receive and Read SMS Messages
- 20. Operating Mode: SMS Text Mode and SMS PDU Mode
- 21. Setting or Reading the Service Center Address / SMSC Address (AT+CSCA)
- 22. Preferred Message Storage (AT+CPMS)
- 23. Writing SMS Messages to Memory / Message Storage (AT+CMGW)
- 24. Deleting SMS Messages from Message Storage (AT+CMGD)
- 25. Sending SMS Messages from a Computer / PC Using AT Commands (AT+CMGS, AT+CMSS)
- 26. Reading SMS Messages from a Message Storage Area Using AT Commands (AT+CMGR, AT+CMGL)
- 27. Appendix A: How to Choose an SMS Service Provider (SMS Gateway Provider, SMS Reseller, SMS Broker)?
- 28. Appendix B: Comparison Table of SMS Service Providers (SMS Gateway Providers, SMS Resellers, SMS Brokers)
- 29. Appendix C: Free Software/Tools and Libraries for Sending and Receiving SMS Messages with a Computer / PC
- 30. Appendix D: GSM 7-bit Default Alphabet Table (with Character Codes of ISO 8859 Latin 1)