AT+ Commands

Introduction to AT Commands

AT commands (short for Attention Commands) are a way to interact and control cellular modems. It provides a standard way to instruct modems on how to behave and where to connect to.

Commands are standardized by the 3GPP. However, different modems adhere to different versions of the specifications and manufacturers often provide additional vendor specific AT commands.

It is therefore recommended to find the AT commands manual from your modem manufacturer so you can configure your specific cellular modem.

AT command basics

AT commands usually start with an AT, followed by the required <command> and sometimes a <value>.

The are 4 types of AT commands: Read, Test, Set and Execute:

• Read AT+<command>?
  Check the current configuration settings of the cellular modem. For example to read the network and cellular technology the modem is using, enter: AT+CSQ?
  
  
• Test AT+<command>=?
  Test the possible input values for specific commands. For example to list the available modes of operations modem, enter: AT+CFUN=?
  
  
• Set AT+<command>=<value>
  Instruct the modem to perform an action, such as activating the modem or enabling roaming.
  For example, the command to set the modem to active is: AT+CFUN=1
  
  
• Execute AT+<x>
  Some commands can be simply executed. For example, the command to check and return the signal quality: AT+CSQ
  
  

Connect to the modem

In order to send AT Commands, you need to connect to the modem first. You may need a program which provides the interface between your computer and the modem.

You can use minicom, screen or miniterm for Linux/MacOS or PuTTY for Windows.

When using Windows, you might need to install a driver to establish a connection. Have a look at the modem manufacturer's website for details about a possible driver.

To test if the connection with the cellular modem has been established, enter AT. When the modem responds with OK you're set.

Before you get start started

You need to reset the modem to its default configuration and activate the modem before starting the configuration process:

Set the error reporting to verbose which allows more descriptive error messages:

Check the status of the SIM card. If you receive an error, the SIM may not be inserted properly or the SIM might be locked with a PIN. Note: a lot of SIMs are not PIN protected by default:

Query device information

Request the modem hardware version:

Request the modem firmware version:

Request the IMSI (International Mobile Subscriber Identity):

Request the ICCID (Integrated Circuit Card ID), which is the identification number of the SIM card:

Network provider and cellular technology settings

The AT Command related to the Network Provider and cellular technology: AT+COPS

Syntax: AT+COPS=<mode>,<format>,<oper>,<AcT>

Read the operator and access technology:

The test command lets the modem perform a network scan:

In Australia, the following PLMN (public land-mobile network),
codes represent the telecommunication carriers:

Check the modem signal strength and signal quality

Request the modem hardware version:

+CSQ returns 2 values separated by a comma. The first value represents the signal strength and provides a value between 0 and 31; higher numbers indicate better signal strength. The second value represents the signal quality indicated by a value between 0 and 7. If AT+CSQ returns 99, the signal is undetectable or unknown.
Note: In my experience in Australia, the second digit always returns 99 regardless of the connection.

Network Configuration

Set the APN to telstra.nbiot

Read the APN configuration:

Set the PDP (packet data protocol) context to active:

Read the APN configuration:

Read Network registration status:

The second variable indicates the registraion status:
0: Not registered
1: Registered, home network
2: Not registered, but the modem is trying to connect
3: Registration denied
4: Unknown (for example, out of coverage)
5: Registered, roaming
90: Not registered due to UICC failure