17. AT Command Operations: Test, Set, Read and Execution
There are four types of AT command operations:
Test operation. A test operation is used to check whether a certain AT command is supported by the GSM/GPRS modem or mobile phone.
Set operation. A set operation is used to change the settings used by the GSM/GPRS modem or mobile phone for certain tasks.
Read operation. A read operation is used to retrieve the current settings used by the GSM/GPRS modem or mobile phone for certain tasks.
Execution operation. An execution operation is used to perform an action or retrieve information/status about the GSM/GPRS modem or mobile phone.
The command syntax for performing an operation will be described in detail in the following sections.
17.1. Test Command -- Checks Whether a Certain AT Command is Supported
A test operation is used to check whether a certain AT command is supported by the GSM/GPRS modem or mobile phone. All extended AT commands support the test operation. The syntax is:
where command is an AT command. When an AT command is used in the above syntax to perform a test operation, it is called a test command.
Here is an example. The AT command +CGMI (command name in text: Request Manufacturer Identification) is used to get the manufacturer name of the GSM/GPRS modem or mobile phone. To test whether +CGMI is supported, you can make use of the test command "+CGMI=?". The complete command line that should be entered is:
If the GSM/GPRS modem or mobile phone supports the AT command +CGMI, the result code "OK" will be returned, like this:
If the GSM/GPRS modem or mobile phone does not support the AT command +CGMI, the result code "ERROR" will be returned, like this:
In the above example, the AT command +CGMI does not have any parameters. If the AT command to be tested has parameter(s), the parameter value(s) supported by the GSM/GPRS modem or mobile phone may be printed additionally. Below is an example that illustrates the format of the response. +COMMAND1 is a fictitious AT command that has four parameters.
The supported values of each of the four parameters are enclosed in parentheses. Commas are used to delimit the parentheses and the values inside parentheses. A hyphen is used to indicate a range of values. The values inside parentheses can be of the string type.
In the above example, the response of the test command "+COMMAND1=?" provides us the following information:
(0,1). The first parameter accepts either 0 or 1.
(0-10). The second parameter accepts any integer between 0 and 10.
(0,1,5-10). The third parameter accepts 0, 1 or any integer between 5 and 10.
("GSM","UCS2"). The fourth parameter accepts either the string "GSM" or "UCS2".
To a few AT commands, the test operation does not return the parameter values supported. Instead, it returns the values that are allowed to appear in the information response of the AT command. An example is the +CBC AT command (command name in text: Battery Charge). The +CBC command is used to retrieve the connection status and charge level of the battery of the mobile device. Two values are returned in the information response of the +CBC AT command. The format is:
For example, if the battery is placed in the mobile device with no charger connected and the charge level is 80%, the result of the execution of the +CBC AT command will be:
If you run the test command "+CBC=?", all the supported values that are allowed to appear in the connection status field and charge level field will be provided. With my Nokia 6021, the result is:
"(0,1)" means the connection status field in the information response of the +CBC AT command can contain either 0 or 1, while "(0-100)" means the charge level field can contain any integer between 0 and 100.
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- 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)