SARA-G3 and SARA-U2 series - System Integration Manual
UBX-13000995 - R26 System description
Page 38 of 217
1.6.1.4 General considerations for the switch-on procedure
A greeting text can be activated by means of the +CSGT AT command (see the u-blox AT Commands Manual
[3]) to notify the external application that the module is ready to operate (i.e. ready to reply to AT commands)
and that the first AT command can be sent to the module. In this case, the UART autobauding must be disabled
to let the module send the greeting text: the UART must be configured at fixed baud rate (the baud rate of the
application processor) instead of the default autobauding, otherwise the module does not know the baud rate
to be used for sending the greeting text (or any other URC) at the end of the internal boot sequence.
As an alternative starting procedure, after the interfaces’ configuration phase, the application can start sending
AT commands and wait for the response with a 30 second timeout; iterate it 4 times without resetting or
removing the VCC supply of the module, and then run the application.
The Internal Reset signal is not available on a module pin, but the host application can monitor:
o The V_INT pin to sense the start of the module power-on sequence.
o The USB interface to sense the start of the SARA-U2 modules power-on sequence: the module, as a
USB device, informs the host of the attach event via a reply on its status change pipe for proper bus
enumeration process according to the Universal Serial Bus Revision 2.0 specification [14].
Before the switch-on of the generic digital interface supply source (V_INT) of the module, no voltage
driven by an external application should be applied to any generic digital interface of the module.
Before the modules are fully ready to operate, the host application processor should not send any AT
command over the AT communication module interfaces (USB, UART).
The duration of SARA-G3 and SARA-U2 series modules’ switch-on routine can vary depending on the
application / network settings and the concurrent module activities.
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