Let's take a deep dive into the world of AT Commands: what are they and what are the most common AT commands for 2G, 3G and 4G cellular modules? We will try to answer these and many more questions in this complete guide about AT commands for cellular networks.
What are AT commands?
The first step to diving into the Internet of Things is connecting your hardware to a modem. The connection between a modem and your hardware is achieved using AT commands. AT commands are a short text command language dating back to 1981, originally developed for Hayes smart modems and later used in dial-up modems in the 1990s.
AT commands enable you to control everything around the modem, device, and SIM:
Wake the device or put it in sleep mode
Scan for and register to available networks and radio types
Get updates about network condition changes
Read/send SMS and USSD
Send data (TCP/IP)
Get hardware and SIM information (IMEI, IMSI, etc.)
and much more
To get started, we will talk about the syntax or the types of AT commands that can be sent to the modem.
What is the syntax of AT commands?
AT Commands usually have a standardized syntax rule - most commands have three different types: write, read, and test. And then there are also others that can be executed just to retrieve information. All standard AT commands start with AT+<command>
. The response to the commands do not contain AT and only use +<command>:
1.
Write
:AT+<x>=<…>
Sets the user-definable parameter values of the modem
The expected response is usually only "OK"
Example: AT+CREG=1
– meaning enable network registration report
2.
Read:
AT+<x>?
Returns the settings of the modem
Example: AT+CREG?
Response: +CREG: 1,1
– meaning currently reports are configured to be enabled and the device is registered on the home network
AT+<x>=?
Checks supported configurations / services of the modem
Example: AT+CREG=?
Response: +CREG: (0-2)
– meaning that 0,1,2 can be set in the AT+CREG command
AT+<x>
Retrieve information or execute command
Example: AT+CCID
Response: +CCID:8988303000005737285 - returning the SIM card identifier (ICCID)
Then there are also reports that can be generated on status changes for several commands often called unsolicited results code (reports). For example when the network registration changes. These reports have a similar format to the read command but sometimes differ on a couple of parameters.
Whereas AT commands are standardized in 3GPP TS 27.005 and 27.007 and all manufacturers need to implement them, there can be differences based on the modem type and vendor.
Based on the modem type - for e.g., some power saving commands are only available on newer versions that also have the functionality. Parameters may also differ because the modem does not support this specific radio type configuration or error code.
Often manufacturers introduce additional proprietary AT commands that either have new functionality or enhance existing AT commands. While these commands can be powerful, considerations for cross-vendor firmware need to be taken.
Usually vendor proprietary commands are identifiable by a slightly changed command syntax in the beginning.
Quectel - start with AT+Q - e.g. AT+QCFG
U-Blox - start with AT+U - e.g. AT+UDCONF
Telit - start with AT “@”, “#”, “$” or “*” - e.g. AT@CLCK
Nordic - start with AT% - e.g
. AT%XSNRSQAT+ZCELLINFO
Every modem should have a detailed description of its AT commands in an AT command guide. Nevertheless, you can also check the list of available AT commands with an AT command itself: AT+CLAC
In the standard configuration, the AT-Command response is short: OK and ERROR.
For getting a more detailed output of what caused the error you can use the command AT+CMEE=1 or AT+CMEE=2.
The error will then either start with +CMS ERROR: xxx (indicating a network error) or +CME ERROR: xxx (indicating a device error)
AT+CMEE=1 - each error message includes an error code as described 3GPP TS 27.007 Ch. 9.2. For example, the module will return +CME ERROR: 11 -
meaning the SIM PIN is required.
AT+CMEE=2 - if the modem supports it, then the error message includes a string expression of the error. For example +CME ERROR: SIM PIN required
Basic commands to get information about the modem and SIM card
The below commands do not have a read or test command and no parameters - they only execute commands that return information.
Name
AT Command
Description
Get manufacturer
AT+CGMI
Returns string representation of the manufacturer
Get model
AT+CGMM
Returns the model of the modem.
Get firmware
AT+CGMRReturns firmware revision
Get IMEI
AT+GSN
Retrieves the International Mobile Equipment Identity of the module
Get IMSI
AT+CIMI
Returns the current used IMSI
GET ICCID
AT+CCID
Returns the ICCID of the SIM
GET MSISDN
AT+CNUM
Returns the phone number / MSISDN of the device
EMnify SIMs come with the SIM PIN deactivated so they work in devices that do not have a screen or interface to enter the PIN (e.g. GPS tracker). Below you have examples on how to activate and re-activate the use of the SIM PIN.
The two commands used for managing SIM PIN are AT+CPIN and AT+CLCK.
To remove the check for the SIM PIN:
AT+CPIN? // check which PIN required
+CPIN=SIM PIN // response = SIM pin code required
AT+CPIN=1234 // enter current PIN
OK
AT+CLCK=”SC”,0,”1234″ // remove SIM PIN request at startup - reboot needed
OK
To add the check for SIM PIN:
AT+CPIN? // check if and which PIN required
+CPIN=Ready // no PIN required
AT+CLCK=”SC”,1,”1234″ // PIN activated
You find more information about the CPIN and CLCK command below.
<code>
READY – No PIN required
SIM PIN – PIN code required
SIM PUK – PUK code required
SIM PIN2 – PIN2 code required
SIM PUK2 – PUK2 code required
PH-SIM PIN – USIM depersonalization requiredv1.2.x
PH-NET PIN – Network depersonalization requiredv1.2.x
PH-NETSUB PIN – Network subset depersonalization requiredv1.2.x
PH-SP PIN – Service provider depersonalization requiredv1.2.x
PH-CORP PIN – Corporate depersonalization required
AT+CPIN?
Request which PIN code is required
Response Format:
+CPIN: <code>
Example:
AT+CPIN: READY
AT+CLCK=<fac>,<mode>,<passed>, <class>
Lock or unlock different services on the module.
Example:
AT+CLCK =”AO”,2
<fac> facility
“SC” (U)SIM PIN request at startup
“AO” Bar All Outgoing Calls
“OI” Bar Outgoing International Calls)
“OX” Bar Outgoing International Calls except to Home Country)
“AI” Bar All Incoming Calls
“IR” Bar Incoming Calls when Roaming
“AB” All Barring services
“AG” All outgoing barring services
“AC” All incoming barring services
“FD” SIM card or active application in the UICC (GSM or USIM)
“PF” Lock Phone to the very first inserted SIM/UICC card
“PN” Network Personalization
“PU” Network Subset Personalization
“PP” Service Provider Personalization
“PC” Corporate Personalization
<mode> Defines the operation
0 - unlock facility
1 - lock facility
2 - query status
<password> Password
<class>
1 Voice
2 Data
4 FAX
7 All telephony except SMS (Default)
8 Short message service
16 Data circuit synchronization
32 Data circuit asynchronization 0 OFF 1 ON
While operator selection is often an automated procedure - there are some configurations that you can do to either enforce or prefer specific operators.
Command
Commands and examples
Parameters
AT+COPS
Operator
scan and selection
AT+COPS=<mode>,<format>, <oper>,<AcT>
Forces to register the network
operator
Configuration Examples:
AT+COPS=1,2,"24407"
AT+COPS=0 or AT+COPS=2
AT+COPS=1,2,"24407",8
<mode>:
<format>
<oper>
desired operator in <format><AcT>
Access technology<stat>
Operator statusAT+COPS?
Returns the current mode, the
selected operator, and Access Technology.
Response Format:
+COPS: <mode>,<format>,<oper>,<AcT>
Example Response:
+COPS: 0,0,“ Telekom.de”,0
AT+COPS=?
Returns / scans the list of available operators.
Response Format:
<stat>, long alphanumeric <oper>,
short alphanumeric <oper>, numeric <oper>, <AcT>
Example Response:
+COPS: (3,"Telekom.de","TDG","26201",2),
(1,"E-Plus","E-Plus","26203",2),(3,"Vodafone.de","Vodafone", "26202",2),(3,"Telekom.de","TDG","26201",7)
AT+CPLS
AT+CPLS=<list>
Selects which file shall be used for preferred PLMN list
Example:
AT+CPLS=0
On the SIM there are file to manage operator and radio type preference. These can be set by the user, operator or home network. These files usually start with EFxxxx
<list>: integer type
0: User controlled PLMN selector with Access Technology EFPLMNwAcT, if not found in the SIM/UICC then PLMN preferred list EFPLMNsel
1: Operator controlled PLMN selector with Access Technology EFOPLMNwAcT
2: HPLMN selector with Access Technology EFHPLMNwAcT
AT+CPLS?
Returns the selected PLMN selector list from the SIM/USIM.
Example Response
+CPLS: 0
AT+CPLS=?
Returns list of supported <list>
Example response:
+CPLS: (0-2)
AT+CPOL
User Preferred PLMN list
configuration
(only when CPLS=0)
AT+CPOL=<index>,<format>,<oper>,<GSM_AcT>, <GSM_Compact_AcT>,<UTRAN_AcT>,<EUTRAN_AcT>
Set preferred operator list on the SIM
Config example:
AT+CPOL=50,2,"22210",1,0,1,0
The first index indicates the highest priority and the n
thindex indicates the lowest
AT+CPOL?
Returns all entries from the SIM/USIM EFPLMNwAcT or EFPLMNsel
Response format:
<index1>,<format>,<oper1>,<GSM_AcT1>,<GSM_Compact_AcT1>,<UTRAN_AcT1>,<E-UTRAN_AcT1>
Example Response:
+CPOL: 1,2,"26201",1,0,1,0 +CPOL: 2,2,"21401",1,0,1,0
…
AT+COPN
List all known operators
AT+COPN
Lists all the known operators that can be set by AT+CPOL
Example Reponse
+COPN: "90114","AeroMobile"
…
+COPN: "22210","vodafone IT"
AT+CREG
AT+CGREG
AT+CEGREG
Network registration report
AT+CREG applies to GSM/UMTS CS domain
AT+CGREG
applies for GPRS/UMTS PS domain (GPRS)
AT+CEREG applies for LTE
Some LTE only modules may show registration status also for CREG and CGREG based on backwards compatibility
The syntax for CREG, CGREG, CEGREG is the similar- here explained with AT+CREG
AT+CREG =<n>
Set result code output. Triggers status change reports in different formats.
For <n>=1: +CREG:<stat>
For <n>=2: +CREG: <stat><lac>,<ci>,<AcT>
For <n>=3: +CREG: <stat>,<lac>,<ci>,<AcT>,<cause_type>,<reject_cause>
For <n>=4 or 5 - additional parameters modem specific
Config Example:
AT+CREG=1
<n> Report configuration
0 – Disable network registration unsolicited results code reports
1 – Enable network registration unsolicited result code reports
2 – Enable network registration and location information in reports <lac/tac/rac><ci><AcT>
3 - enable also <cause_type>,<reject_cause> in reports
4 / 5 - dependent on module there can be additional parameters <rac>, <ActiveTime>,<P-RAU>,<GPRS-READY-timer> (only applies to AT+CGREG and CEREG)
<stat>:
0 - not registered, MT is not searching
1 - registered, home network
2 - not registered, MT is searching
3 - registration denied
4 - unknown (e.g. out of coverage)
5 - registered, roaming
<AcT>: Access Type
0 - GSM 1 - GSM Compact
2 - UTRAN 3 - GSM w/EGPRS
4 - HSDPA 5 UTRAN HSUPA
6 - UTRAN w/HSDPA and HSUPA
7 - E-UTRAN
8 – LTE-M
9 - NB-IoT
<lac/tac/rac> Location Area / Tracking Area / Routing Area Code
<ci> Cell ID
<active time> Active Time value (T3324) for Power Save Mode
<P-RAU> period to send RAU/TAU
The syntax for CREG, CGREG, CEGREG is the similar- here explained with AT+CREG
AT+CREG?
Return Current Registration Status
Response Examples:
For <n>=1: CREG: <n><stat>
+CREG: 1,1
for <n>=2: +CREG: <n>,<stat><lac>,<ci>,<AcT>
+CREG: 2,5,"2387","01DB7C01", 2
For n=3: +CREG: <n>,<stat>,<lac>,<ci>,<AcT>,<cause_type>,<reject_cause>
AT+CREG =?
Returns values supported for <n> result code configuration
Example Response
+CREG: (0-3)
Command
Commands and examples
Parameters
AT+CSQAT+CSQ
Reads the signal quality for the connected technology.
Response Format:
+CSQ: <rssi>,<qual>
Example Response:
+CSQ: 21,3
<rssi> received signal strength RSSI values
0: 113 dBm or less
1: 111 dBm
2...30: 109... 53 dBm
31: 51 dBm or greater
99 - not known or not detectable
<qual> For 2G – Bit Error rate ( ~assumed value)
0: BER < 0,2 % ~0,14 %
1: 0,2 % < BER < 0,4 % ~0,28 %
2: 0,4 % < BER < 0,8 % ~0,57 %
3: 0,8 % < BER < 1,6 % ~1,13 %
4: 1,6 % < BER < 3,2 % ~2,26 %
5: 3,2 % < BER < 6,4 % ~4,53 %
6: 6,4 % < BER < 12,8 % ~9,05 %
7: 12,8 % < BER ~18,10 %
99: not detectable
<qual> For 3G - EcNo
0: ECN0_LEV >= 44
1: 38 <= ECNO_LEV < 44
2: 32 <= ECNO_LEV < 38
3..5 14 <= ECNO_LEV < 32
6: 8 <= ECNO_LEV < 14
7: ECNO_LEV < 8
<qual> For LTE/NB-IoT/LTE-M - RSRQ
0: RSRQ_LEV < 5
1: 5 <= RSRQ_LEV < 10
2: 10 <= RSRQ_LEV < 14
3..5: 14 <= RSRQ_LEV < 26
6: 26 <= RSRQ_LEV < 30
7: RSRQ _LEV >= 30
<rxlev> RSSI with 1dbm steps
0: less than -110 dBm
1..62: from -110 to -49 dBm
63: -48 dBm or greater
<ber> - Bit Error Rate as above for 2G
<rscp> RSCP with 1dBm steps
0: less than -120 dBm
1..95: from -120 dBm to -26 dBm
96: -25 dBm or greater
AT+CSQ=?
Returns list of supported parameters <rssi>,<qual>
Example Response
+CSQ: (0-31,99),(0-7,99)
AT+CESQ
Extended signal quality
AT+CESQ
Return signal quality for all radio types the module can monitor.
Response format:
+CESQ: <rxlev>,<ber>,<rscp>,<ecn0>,<rsrq>,<rsrp>
Example Response:
AT+CESQ=?
Returns list of supported parameters value ranges <rxlev>,<ber>, <rscp>, ecno>, <rsrp>, <rsrq>
Example Response:
+CESQ: (0-63,99),(0-7,99),(0-96, 255),(0-49,255),(0-34,255),(0-97, 255)
Command
Commands and examples
Parameters
AT+ CGDCONT<AT+CGDCONT=<cid>,<PDP_type>,<APN>,<PDP_addr>,<data_comp>,<head_comp>
Set the parameters for the PDP context.
Example
AT+CGDCONT=1,"IP","em",
"0.0.0.0",0,0
<cid> PDP context identifier
<PDP_type> - Packet Data Protocol type as string
"IP", “PPP” , “IPV6”, “IPV4V6”
<APN> - Access Point Name string for EMnify "em"
<PDP_addr> (IP) Address identifying the mobile terminal. EMnify assigns private static IPs - so 0.0.0.0 is fine
<d_comp> - controls PDP data compression - for SNDCP
0 OFF
1 ON
2 V.42bis
3 V.44
<h_comp> - controls PDP header compression
0 - off
1 – on
2 - RFC1144 for SNDCP only
3 - RFC2507
4 - RFC3095 (applicable for PDCP only)
AT+CGDCONT?
Returns list of current PDP definitions
Response Format:
+CGDCONT: <cid>,<PDP_type>,<APN>,<PDP_addr>, <data_comp>,<head_comp>
Example Response:
+CGDCONT: 1,"IP","em","0.0.0.0",0,0,0,0
2,"IPV4V6","em", "0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0" ,0,0,0,0
AT+CGACT
AT+CGACT=<state>,<cid>
Activate or deactivate PDP context
Example:
AT+CGACT=1,1
<state>
0 - deactivate
1 - activate
<cid> PDP context ID
AT+CGACT?
Read status of PDP contexts
Response format
+CGACT<state>,<cid>
Example Response:
+CGACT=1,1
These were some of the standard AT commands that all modems support. They let you configure and have control over your cellular communication. Many manufacturer-specific AT commands exist which let you optimize the communication. We will talk about these in another blog post.
For more information Bulk Sms Modem, please get in touch with us!
Wave Washers Selection belleville washers hot dipped galvanized water tank hot dipped galvanized water tank CAS 26264-06-2 pwr drill pwr drill Smart sensor flush valve Smart sensor flush valve ruthenium chloride hydrate Distribution Panel Commissioning Distribution Panel Commissioning Electrical Tracing on Pipe Electrical Tracing on Pipe SOM Core Board SOM for interactive self-service terminal