Monday, June 17, 2024

All You Wanted To Know About AT And GSM AT Commands

- Advertisement -


What are AT commands?

AT commands are commands which are used to control the modems where AT stands for Attention. These commands were derived from Hayes commands which were used by the Hayes smart modems. Every wireless, as well as the dial up modems, require an AT command to interact with a computer machine. These AT commands along with other extended commands also require Hayes command set as a subset.


The AT commands can be used with GSM module and GPRS MODEMs or phone to access these services and information:

- Advertisement -
  • SMS
  • MMS
  • Fax
  • Voice link and other data over mobile network
  • Information and configuration concerning the mobile devices or MODEM and SIM card.

Types of AT Command

There are 4 basic types of AT commands:

  1. Test: The test command is utilised to check the compatibility of a command by a modem.


2. Read: Read command is used for extracting the mobile or modem settings required for operations.


3. Set: This commands is used to make changes into mobile phone or modem settings required for the operation.

SYNTAX: AT=value1, value2, …, valueN

4. Execution: As the name suggests, this command is used to execute the said operation.

SYNTAX: AT=parameter1, parameter2, …, parameterN

Most Commonly Used AT Commands

The below 7 are the most commonly used AT commands:

  1. AT: Used to check the interaction between the computer and the module. This command is usually replied with an OK if the port and the module can connect correctly, else wise it comes back with a result code ERROR.

2. +CMGF:Used to setup the SMS mode. By adding 1 or 0 with the command text or PDU mode can be selected. Here the text mode is easy to operate although it only allows a few limited features of SMS. Where as the PDU mode allows a more detailed access to the SMS service, although to use this you require some basic knowledge of TDPU.


3. +CMGS: Used to send SMS to a particular phone number

SYNTAX: AT+CMGS= serial number of message to be send.

4. ATD: Used to make call to a particular number


5. ATA: Used to answer the incoming calls. The calls are denoted by a message ‘RING’ which duplicated for every ring of the call. After the call ends a message saying ‘NO CARRIER’ is displayed.


6. +CMGW: Used to store a message in the SIM. After the execution of the command, the ‘>’ sign appears in the next line where the message can be entered.

SYNTAX: AT+CMGW=” Phone number”> Message to be stored Ctrl+z

7. ATH:this commaned is utilized to disconnect a remote user with the GSM module.


List of AT Commands

Command Description
AT Checking communication between the module and computer.
Call control:
Command Description
ATA Answer command
ATD Dial command
ATH Hang up call
ATL Monitor speaker loudness
ATM Monitor speaker mode
ATO Go on-line
ATP Set pulse dial as default
ATT Set tone dial as default
AT+CSTA Select type of address
AT+CRC Cellular result codes
Data card Control:
Command Description
ATI Identification
ATS Select an S-register
ATZ Recall stored profile
AT&F Restore factory settings
AT&V View active configuration
AT&W Store parameters in given profile
AT&Y Select Set as power up option
AT+CLCK Facility lock command
AT+COLP Connected line identification presentation
AT+GCAP Request complete capabilities list
AT+GMI Request manufacturer identification
AT+GMM Request model identification
AT+GMR Request revision identification
AT+GSN Request product serial number identification (IMEI)
Phone control:
Command Description
AT+CBC Battery charge
AT+CGMI Request manufacturer identification
AT+CGMM Request model identification
AT+CGMR Request revision identification
AT+CGSN Request product serial number identification
AT+CMEE Report mobile equipment error
AT+CPAS Phone activity status
AT+CPBF Find phone book entries
AT+CPBR Read phone book entry
AT+CPBS Select phone book memory storage
AT+CPBW Write phone book entry
AT+CSCS Select TE character set
AT+CSQ Signal quality
Computer data interface:
Command Description
ATE Command Echo
ATQ Result code suppression
ATV Define response format
ATX Response range selection
AT&C Define DCD usage
AT&D Define DTR usage
AT&K Select flow control
AT&Q Define communications mode option
AT&S Define DSR option
AT+ICF DTE-DCE character framing
AT+IFC DTE-DCE Local flow control
AT+IPR Fixed DTE rate
Command Description
AT+CLIP Calling line identification presentation
AT+CR Service reporting control
AT+DR Data compression reporting
AT+ILRR DTE-DCE local rate reporting
Network Communication parameter:
Command Description
ATB Communications standard option
AT+CBST Select bearer service type
AT+CEER Extended error report
AT+CRLP Radio link protocol
AT+DS Data compression
Command Description
A/ Re-execute command line
AT? Command help
AT*C Start SMS interpreter
AT*T Enter SMS block mode protocol
AT*V Activate V.25bis mode
AT*NOKIATEST Test command
AT+CESP Enter SMS block mode protocol
SMS Text mode:
Command Description
AT+CSMS Select message service
AT+CPMS Preferred message storage
AT+CMGF Message format
AT+CSCA Service centre address
AT+CSMP Set text mode parameters
AT+CSDH Show text mode parameters
AT+CSCB Select cell broadcast message types
AT+CSAS Save settings
AT+CRES Restore settings
AT+CNMI New message indications to TE
AT+CMGL List messages
AT+CMGR Read message
AT+CMGS Send message
AT+CMSS Send message from storage
AT+CMGW Write message to memory
AT+CMGD Delete message
SMS PDU mode:
Command Description
AT+CMGL List Messages
AT+CMGR Read message
AT+CMGS Send message



to memory

This article was first published on 26 Dec 2013 and was recently updated on 29 January 2019.


  1. How can I increase my bandwidth in end to end communication by mobile please.
    I already built 2 cryptosystem and my problem is bandwidth of two handset mobiles which is not enough bandwidth between operator and mobile side.

    Thanks in advance


Unique DIY Projects

Electronics News

Truly Innovative Tech

MOst Popular Videos

Electronics Components