to AT Commands
commands are instructions used to control a modem. AT is the
abbreviation of ATtention. Every command line starts with "AT"
or "at". That's why modem commands are called AT commands.
Many of the commands that are used to control wired dial-up modems,
such as ATD (Dial), ATA (Answer), ATH (Hook control) and ATO (Return
to online data state), are also supported by GSM/GPRS modems and
mobile phones. Besides this common AT command set, GSM/GPRS modems
and mobile phones support an AT command set that is specific to the
GSM technology, which includes SMS-related commands like AT+CMGS
(Send SMS message), AT+CMSS (Send SMS message from storage), AT+CMGL
(List SMS messages) and AT+CMGR (Read SMS messages).
that the starting "AT" is the prefix that informs the modem
about the start of a command line. It is not part of the AT command
name. For example, D is the actual AT command name in ATD and +CMGS
is the actual AT command name in AT+CMGS. However, some books and web
sites use them interchangeably as the name of an AT command.
are some of the tasks that can be done using AT commands with a
GSM/GPRS modem or mobile phone:
basic information about the mobile phone or GSM/GPRS modem. For
example, name of manufacturer (AT+CGMI), model number (AT+CGMM),
IMEI number (International Mobile Equipment Identity) (AT+CGSN) and
software version (AT+CGMR).
basic information about the subscriber. For example, MSISDN
(AT+CNUM) and IMSI number (International Mobile Subscriber Identity)
the current status of the mobile phone or GSM/GPRS modem. For
example, mobile phone activity status (AT+CPAS), mobile network
registration status (AT+CREG), radio signal strength (AT+CSQ),
battery charge level and battery charging status (AT+CBC).
a data connection or voice connection to a remote modem (ATD, ATA,
and receive fax (ATD, ATA, AT+F*).
(AT+CMGS, AT+CMSS), read (AT+CMGR, AT+CMGL), write (AT+CMGW) or
delete (AT+CMGD) SMS messages and obtain notifications of newly
received SMS messages (AT+CNMI).
(AT+CPBR), write (AT+CPBW) or search (AT+CPBF) phonebook entries.
security-related tasks, such as opening or closing facility locks
(AT+CLCK), checking whether a facility is locked (AT+CLCK) and
changing passwords (AT+CPWD).
(Facility lock examples: SIM lock
[a password must be given to the SIM card every time the mobile
phone is switched on] and PH-SIM lock [a certain SIM card is
associated with the mobile phone. To use other SIM cards with the
mobile phone, a password must be entered.])
the presentation of result codes / error messages of AT commands.
For example, you can control whether to enable certain error
messages (AT+CMEE) and whether error messages should be displayed in
numeric format or verbose format (AT+CMEE=1 or AT+CMEE=2).
or change the configurations of the mobile phone or GSM/GPRS modem.
For example, change the GSM network (AT+COPS), bearer service type
(AT+CBST), radio link protocol parameters (AT+CRLP), SMS center
address (AT+CSCA) and storage of SMS messages (AT+CPMS).
and restore configurations of the mobile phone or GSM/GPRS modem.
For example, save (AT+CSAS) and restore (AT+CRES) settings related
to SMS messaging such as the SMS center address.
that mobile phone manufacturers usually do not implement all AT
commands, command parameters and parameter values in their mobile
phones. Also, the behavior of the implemented AT commands may be
different from that defined in the standard. In general, GSM/GPRS
modems designed for wireless applications have better support of AT
commands than ordinary mobile phones.
addition, some AT commands require the support of mobile network
operators. For example, SMS over GPRS can be enabled on some GPRS
mobile phones and GPRS modems with the +CGSMS command (command name
in text: Select Service for MO SMS Messages). But if the mobile
network operator does not support the transmission of SMS over GPRS,
you cannot use this feature.
Commands and Extended Commands
are two types of AT commands: basic commands and extended commands.
commands are AT commands that do not start with "+". For
example, D (Dial), A (Answer), H (Hook control) and O (Return to
online data state) are basic commands.
commands are AT commands that start with "+". All GSM AT
commands are extended commands. For example, +CMGS (Send SMS
message), +CMSS (Send SMS message from storage), +CMGL (List SMS
messages) and +CMGR (Read SMS messages) are extended commands.
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