u-blox SARA-R4 Series System Integration Manual

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SARA-R4 series - System Integration ManualUBX-16029218 - R06 System descriptionPage 21 of 102Figure 7 describes the SARA-R4 series modules switch-off sequence started by means of the PWR_ON input pin,allowing storage of current parameter settings in the module’s non-volatile memory and a proper networkdetach, with the following phases: A low pulse with appropriate time duration (see SARA-R4 series Data Sheet [1]) is applied at the PWR_ONinput pin. At the end of the switch-off routine, all the digital pins are tri-stated and all the internal voltage regulatorsare turned off, including the generic digital interfaces supply (V_INT). Then, the module remains in power-off mode as long as a switch on event does not occur (e.g. applying aproper low level to the PWR_ON input ), and enters not-powered mode if the VCC supply is removed.VCCPWR_ONRESET_NV_INTInternal ResetSystem StateBB Pads StateOFFTristate / FloatingONOperational -> TristateOperational0 s ~2.5 s ~5 sThe module startsthe switch-off routineVCC can beremovedFigure 7: SARA-R4 series switch-off sequence by means of PWR_ON pinThe Internal Reset signal is not available on a module pin, but it is recommended to monitor the V_INTpin to sense the end of the switch-off sequence: VCC supply can be removed only after V_INT goes low.The duration of each phase in the SARA-R4 series modules’ switch-off routines can largely vary dependingon the application / network settings and the concurrent module activities.1.6.3 Module resetSARA-R4 series modules can be properly reset (rebooted) by: AT+CFUN command (see SARA-R4 series AT Commands Manual [2]).In the case listed above an “internal” or “software” reset of the module is executed: the current parametersettings are saved in the module’s non-volatile memory and a proper network detach is performed.An abrupt hardware shutdown occurs on SARA-R4 series modules when a low level is applied on RESET_N inputpin for a valid time period. In this case, the current parameter settings are not saved in the module’s non-volatilememory and a proper network detach is not performed. Then, the module remains in power-off mode as longas a switch on event does not occur applying a proper low level to the PWR_ON input.It is highly recommended to avoid an abrupt hardware shutdown of the module by forcing a low level onthe RESET_N input during modules normal operation: the RESET_N line should be set low only if reset orshutdown via AT commands fails or if the module does not provide a reply to a specific AT commandafter a time period longer than the one defined in the SARA-R4 series AT Commands Manual [2].The RESET_N input pin is equipped with an internal pull-up to a 1.8 V supply domain. Detailed electricalcharacteristics with voltages and timings are described in SARA-R4 series Data Sheet [1].