SARA-R4/N4 series-AT Commands Manual
UBX-17003787 - R09
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2General operation
Page 16 of 307
2î™–î™–î™–î™–General operation
2.1î™–î™–î™–î™–Start up and initialization
The characteristics of the boot of the cellular device vary from module to module and are described in the
corresponding System Integration Manual; during this phase the module might be not responsive on the AT
interface until all necessary SW modules have been installed (e.g. USB drivers); monitoring of the greeting text,
where supported, can help in detecting the successful end of the boot phase.
A complete start up to be able to operate on the cellular network can take place only with a SIM card.
If the SIM card has enabled the PIN check, some commands answer with "+CME ERROR: SIM PIN required"
and most cellular functionalities are not started. After entering the required PIN via the +CPIN command, or
if booting with a SIM with disabled PIN check, SIM initialization is carried out and a lot of SIM files are read:
it is possible that some commands (e.g. phonebook AT commands) are affected by this preliminary phase,
resulting in a temporary error response.
2.1.1î™–î™–î™–î™–Auto-registration
If the +COPS <mode> parameter in the profiles or in NVM is left to its factory-programmed value 0 or set to 1,
after SIM initialization, all u-blox modules will automatically perform PLMN selection and registration for circuit
switched/non EPS services as well as packet switched/EPS services. Auto-registration (sometimes called also
"auto-COPS", not to be confused with automatic <mode>=0) will be triggered also at SIM insertion, for modules
supporting SIM hot insertion, or at SIM driver recovery, occurring when the communication with the SIM card
is re-established by the module after an unrecoverable error, caused e.g. by mechanical vibrations or electrical
interference. If no SIM is inserted in the module, the module will anyway select a cell of the cellular network and
try to maintain synchronization with it in limited service.
The radio
access technology selected
by the module
at start up
is defined by
the <PreferredAct> parameter
of
the +URAT command; afterwards the module will reselect the RAT based on the requirements of the cellular
standards it complies with and it is not possible to force it to remain in a given RAT unless it is locked on it via
+URAT or on a specific cell via +UCELLLOCK (if supported).
The user can retrieve the result of the auto-registration by polling the registration status commands (e.g.
+CREG/+CGREG/+CEREG/+CIREG) or enabling their unsolicited notifications. If auto-COPS is running, at boot
time or at SIM insertion, network service commands issued by the user might have a longer response time than
expected; this is particularly visible when the module is switched on in a jammed condition, or with a roaming
SIM card that shall perform several registration attempts before gaining access to a VPLMN. In case of failures
of the automatic registration whose cause cannot be retrieved via +CEER, it is suggested to disable auto-COPS
starting the module in +COPS:2 or in airplane mode +CFUN:4 and trigger registration with AT commands.
2.1.2î™–î™–î™–î™–Operational restrictions
Operational restrictions may derive from several settings: PIN required, SIM lock, invalidation of the IMEI
or SIM credentials by the Mobile Network Operator (MNO) during the registration procedure, FDN enabled.
Restrictions to access the network are also applied by the module in any one of these conditions:
• In eCall only state (for all modules supporting the eCall feature)
• In minimum functionality power modes (+CFUN: 0, +CFUN: 4, +CFUN: 19, +CFUN: 127), and even if the
module is restarted in +CFUN: 4 or +CFUN: 19 modes, because they are persistent
In case the module is in operational restricted state, it may reject all or specific service requests (e.g. operator
selection, connection establishment).
2.2î™–î™–î™–î™–AT commands types
2.2.1î™–î™–î™–î™–Action command
An action command forces the DCE to print information text or execute a specific action for the command.
A typical example of this command type is the provision of the factory-programmed settings of the DCE like
manufacturer name, firmware version, etc.
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