CELLULAR > GSM / UMTS > AT Commands

AT Commands

AT Commands (or Hayes commands) allow a user to communicate directly with a modem. Compared to using GUI-based software (eg. from the manufacturer or service provider) AT Commands are more complex but also allow for a wider range of settings control.

For GSM/UMTS/HSPA modems, 3GPP specifies a command set:
http://www.3gpp.org/ftp/Specs/html-info/27007.htm

To connect to your modem with HyperTerminal or PUTTY in Windows, use the following:



1- Find what port your modem is using:
Start -> Control Panel -> Phone and Modem Settings -> Modem

2- In Windows XP/Vista using PUTTY

Download PUTTY. No installation is necessary, just double click to open.
http://the.earth.li/~sgtatham/putty/latest/x86/putty.exe

On "Session" page (opens by default), select "Serial" button, then enter COM port number and 115200 bit rate (bit rate is not really important). Then click "Open".

In the terminal type ATE1 to echo characters.

Type ATI to confirm you are on correct modem (device name should be returned).
AT Commands are not case sensitive, "ATI" or "ati" provide the same results.

(Optional) In Windows XP using HyperTerminal:

Note: HyperTerminal has been removed in Windows Vista! You should either use PUTTY or take these files from a WinXP system to use HyperTerminal in Vista: hypertrm.dll and hypertrm.exe


Start -> All Programs -> Accessorises -> Communications -> HyperTerminal
(Icon and name is not important) -> OK (Select COM Port from DropDown Box) -> OK (Change "Bits per seconds" to 115200) ->OK


(Optional: To echo typed characters in display) -> File -> Properties -> Settings -> ASCII Setup -> (Tick) Echo Typed Characters Locally -> OK

...or type ATE1 in the terminal (also echos characters).

Type ATI to confirm you are on correct modem (device name should be returned).
AT Commands are not case sensitive, "ATI" or "ati" provide the same results.


3- Go!

You are now connected to the modem and can begin typing commands to see modem information, and change some settings as well. Most AT commands are standardized, but some are optional or vary by manufacturer. Some manufacturers provide AT guides for their equipment, for example Sierra Wireless provides guides:

For GSM modems:
http://www.sierrawireless.com/documents/support/2130213_GSM_AT_Command_Ref_r3.2.pdf

For UMTS modems:
http://www.sierrawireless.com/resources/documents/support/2130617_Supported_AT_Command_Reference_Rev_2.1.pdf


Every AT command begins with "AT+" followed by the command. If the command ends in "?" (read) or "=?" (test) it is asking the modem for information. Otherwise it is a command being sent to the modem, with the instructions to send after the "=".

Some example commands are:

To unlock a locked modem:

Command: AT+CLCK="PN",0,"<8 digit unlock code>"
Response: OK
(Note: You must have the 8-digit unlock code from the modem manufacturer or your service provider)

To check radio signal quality:

Command: AT+CSQ
Response: +CSQ: <rssi>,<ber>
Description: Returns signal quality.

RSSI: Higher number = strong signal (ie: [31] is the strongest, [0] is the weakest

BER: Lower number is less interference (ie: [0] is little or no interference, and [7] is alot of interference)

<rssi> Received Signal Strength Indicator
[0] = -113 dBm or less
[1] = -111 dBm
[2] to [30] = -109 to -53 dBm (each <rssi> step represents 2dBm)
[31] = -51 dBm or greater
[99] = not known or not detectable

<ber> Bit Error Rate
In percent [0] to [7]
[99] = not known or not detectable



Network information:

Command: AT+COPS?
Response: +COPS: (<mode>,[<format>,<oper>[,<AcT>]]),…, (<modeN>,[<formatN>,<operN>[,<AcTN>]])

Command: AT+COPS=?
Response: +COPS: <stat>, long <oper>, short <oper>, numeric <oper>, <AcT>

Command: AT+COPS=<mode>,[<format>,<oper>[,<AcT>]]
Response: OK | +CME ERROR

Description: Get/set current GSM/UMTS network operator, list available operators. This can be used to change for example access type and switch network.

<mode>
[0] - Automatic network selection (<oper> ignored)
[1] - Manual network selection, <oper> must be present, <AcT> is optional.
[2] - Deregister from network.
[3] - Set <format only, no registration/deregistration.
[4] - Manual selection with automatic fall back (enters automatic mode if manual selection fails).

<format>
[0] - Long alphanumeric string
[1] - Short alphanumeric string
[2] - Numeric ID

<oper>
String (based on <format>) that identifies the operator.

<stat>
[0] - Unknown
[1] - Available
[2] - Current
[3] - Forbidden

<AcT> Network access type
[0] - GSM
[1] - Compact GSM
[2] - UTRAN
[3] - GSM with EGPRS
[4] - UTRAN with HSDPA
[5] - UTRAN with HSUPA
[6] - UTRAN with HSDPA and HSUPA