User Manual

SARA-R4/N4 series-AT Commands Manual
UBX-17003787 - R11
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2General operation
Page 17 of 308
2.2.2Set command
A set command configures the preferred settings for the specified command. The set command is the only
way to set the preferred settings in the DCE. For some commands it is possible to store the current settings
in the profile or in the non volatile memory and retrieve them in another connection.
2.2.3Read command
A read command provides the current setting of the command parameters. It is used to find out the current
command configuration.
2.2.4Test command
A test command provides the list of the values allowed by each parameter of the command.
2.2.5Unsolicited Result Code (URC)
An unsolicited result code is a string message (provided by the DCE) that is not triggered as a information
text response to a previous AT command and can be output, when enabled, at any time to inform the DTE of
a specific event or status change.
The URC can have the same name of the command that enables it (e.g. +CREG) or can be enabled by another
command (e.g. the +CMTI URC must be enabled by AT+CNMI AT command).
2.2.5.1URCs presentation deferring
Since the URCs are text responses issued by the DCE without being requested by the DTE, their occurrence
is completely uncorrelated to an AT command execution. Therefore, a collision between a URC and an AT
command response might occur and it may lead the DTE to misunderstand the URC as part of the AT
command's text response or viceversa.
The module avoids this collision by delaying the URCs presentation in case the AT command interface is busy.
The AT command interface can be busy in the following cases:
• During a data call (data mode)
• During the execution of an AT command in command or online command mode
The command execution starts when the command line is completed by the command line termination
character and the AT interpreter in the module accepts it; the command execution ends when the final result
code for the command is sent out. Inside this period, the module is not allowed to send the not buffered URCs.
For most of the messages, the DCE needs to be configured whether or not to send a URC. After enabling, for
most of the URCs, if the AT command interface is busy, the pending URCs are buffered and their sending to
the DCE is deferred. The RING indication is always generated as an unsolicited result code. The NO CARRIER
indication is generated as an unsolicited result code when it has not to be considered the final response for
the executing command (e.g.: ATH); in case it is handled as an unsolicited result code, it follows the rule of the
other URCs.
Generally, the buffered URCs are sent to the terminal as soon as the terminal exits the data mode or the
command execution is terminated. An exception to this behavior is implemented for the following URCs
classes:
Class AT command to configure the class
Reception of a new SMS related URCs AT+CNMI AT command
+CIEV URCs AT+CMER AT command
For the above classes, it is possible to select the presentation strategy in case of AT interface busy according
the 3GPP TS 27.007 [2]; the buffering or discarding are the two possible choices (URCs are lost in the latter
case). This is done by means of the corresponding AT command (see the AT command listed in the table above).
If the URCs are enabled or for the three described classes of URCs, the buffered URCs are sent out only when
the AT interface is in idle again; this occurs as soon as:
• The data mode is released (the data call is disconnected)
• The final result code for an AT command is issued
The DTE should wait some time (the recommended value is at least 20 ms) after the reception of an AT
command final result code or URC before issuing a new AT command to give the DCE the opportunity to