16.2. Final Result Code Specific to SMS AT Commands

The final result codes OK and ERROR are available to all AT commands. Unlike OK and ERROR, the +CMS ERROR final result code is only available to SMS AT commands. It notifies you about the occurrence of a message service failure.

16.2.1. The +CMS ERROR Final Result Code -- Notifies the Occurrences and Causes of Message Service Failures

The +CMS ERROR final result code is returned when a message service failure occurs. An error code is provided for programmers to check what causes the message service failure. The +CMS ERROR final result code is specific to SMS AT commands, i.e. the +CMS ERROR final result code will only be outputted by AT commands that are used to perform tasks related to SMS messaging. Below are the SMS AT commands that may output the final result code +CMS ERROR:

• +CMGC (command name in text: Send Command)

• +CMGD (command name in text: Delete Message)

• +CMGL (command name in text: List Messages)

• +CMGR (command name in text: Read Message)

• +CMGS (command name in text: Sending Message)

• +CMGW (command name in text: Write Message to Memory)

• +CMSS (command name in text: Send Message from Storage)

• +CNMA (command name in text: New Message Acknowledgement to ME/TA)

• +CNMI (command name in text: New Message Indications to TE)

• +CPMS (command name in text: Preferred Message Storage)

• +CRES (command name in text: Restore Settings)

• +CSAS (command name in text: Save Settings)

• +CSMS (command name in text: Select Message Service)

The syntax of the +CMS ERROR final result code is:

<CR><LF>+CMS ERROR: error_code<CR><LF>

Just as the final result codes OK and ERROR, the +CMS ERROR final result code always starts and ends with a carriage return character and a linefeed character. error_code is an integer that is associated to a certain error. A list of some error codes and their meanings can be found in "Table of +CMS Error Codes and Their Meanings".

As mentioned earlier, after the execution of a command line, only one final result code is returned. Hence, when an error occurs, you will not find both +CMS ERROR and ERROR in the command response. For errors related to SMS messaging, the +CMS ERROR final result code is returned. For other errors such as invalid command syntax and unsupported AT command, the ERROR final result code is returned as usual.

Below shows some common causes of +CMS errors:

• A SIM card is not present in the GSM/GPRS modem or mobile phone.

• The SIM card requires a password (e.g. PIN, PIN2, PUK and PUK2) but you have not entered it.

• An invalid memory index is assigned to an AT command.

• The memory of the GSM/GPRS modem, mobile phone or SIM card for storing SMS messages is full.

• The SMSC address is unknown or incorrect.

Following is an example that demonstrates the usage of the +CMS ERROR result code. Let's say there is only one SMS text message stored on our Nokia 6021 and it is stored in the memory location at index 1. If we enter the command line "AT+CMGR=11" (it means "to read the SMS message at memory index 11"), Nokia 6021 will return a +CMS error:

AT+CMGR=11<CR>
<CR><LF>+CMS ERROR: 321<CR><LF>

As mentioned earlier, 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 you entered, together with the response returned, will be displayed like this in a terminal program such as HyperTerminal of Microsoft Windows:

AT+CMGR=11
+CMS ERROR: 321

To find out the meaning of the +CMS error code 321, go to "Table of +CMS Error Codes and Their Meanings". From there, we know that the read message operation failed because an invalid memory index was assigned to the AT command +CMGR.

Note that after the occurrence of a +CMS error, the GSM/GPRS modem or mobile phone will not process the remaining AT commands in the command line. Thus, if the command line sent to Nokia 6021 is "AT+CMGR=11;+CGMI" (+CGMI is the AT command for retrieving the manufacturer name of the GSM/GPRS modem or mobile phone), you will get the following result in Windows' HyperTerminal:

AT+CMGR=11;+CGMI
+CMS ERROR: 321

But if the positions of the two AT commands in the command line are exchanged, Nokia 6021 will output the result of the execution of the AT command +CGMI before outputting the +CMS ERROR result code. Below is the result displayed in Windows' HyperTerminal:

AT+CGMI;+CMGR=11
Nokia

+CMS ERROR: 321

16.2.1.1. Table of +CMS Error Codes and Their Meanings

The following table lists some of the +CMS error codes and their meanings.

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