Integration Manual

LISA-U2 series - System Integration Manual
UBX-13001118 - R25 System description Page 43 of 182
1.6.3 Module reset
LISA-U2 series modules can be properly reset (rebooted) by:
 AT+CFUN command (see the u-blox AT Commands Manual [2] for more details).
This command causes an “internal” or “software” reset of the module, causing an asynchronous reset
of the module baseband processor, excluding the integrated Power Management Unit and the RTC
internal block. The V_INT interfaces supply is enabled and each digital pin is set to its internal reset
state (detailed in the pin description table in the LISA-U2 series Data Sheet [1]), the V_BCKP supply
and the RTC block are enabled.
Forcing an “internal” or “software” reset, the current parameter settings are saved in the module’s
non-volatile memory and a clean network detach is performed: this is the proper way to reset the
modules.
An abrupt hardware reset occurs on LISA-U2 series modules when a low level is applied on the
RESET_N input pin for a specific time period. In this case, the current parameter settings are not
saved in the module’s non-volatile memory and a clean network detach is not performed.
☞ It is highly recommended to avoid an abrupt “external” or “hardware” reset of the module by forcing
a low level on the RESET_N input pin during the module normal operation: the RESET_N line should
be set low only if reset or shutdown via AT commands fails or if the module does not provide a reply
to a specific AT command after a time period longer than the one defined in the u-blox AT
Commands Manual [2].
When a low level is applied to the RESET_N input, it causes an “external” or “hardware” reset of the
module, with an asynchronous abrupt reset of the entire module, including the integrated Power
Management Unit, except for the RTC internal block. The V_INT interfaces supply is switched off and
all the digital pins of the modules are tri-stated, but the V_BCKP supply and the RTC block are
enabled.
Forcing an “external” or “hardware” reset, the current parameter settings are not saved in the
module’s non-volatile memory and a clean network detach is not performed.
When RESET_N is released from the low level, the module automatically starts its power-on sequence
from the reset state. The same procedure is followed for the module reset via AT command after
having performed the network detach and the parameter saving in non-volatile memory.
Name
Description
Remarks
RESET_N
External reset input
Internal 10 k pull-up to V_BCKP
Table 18: Reset pin
☞ The RESET_N pin ESD sensitivity rating is 1 kV (Human Body Model according to JESD22-A114F).
Higher protection levels could be required if the line is externally accessible on the application
board. Higher protection levels can be achieved by mounting an ESD protection (e.g. EPCOS
CA05P4S14THSG varistor array) on the line connected to this pin, close to the accessible point.
☞ For more details about RESET_N circuit precautions for ESD immunity, see section 2.5.3.
The electrical characteristics of RESET_N are different from the other digital I/O interfaces. The
detailed electrical characteristics are described in the LISA-U2 series Data Sheet [1].
RESET_N is pulled high by an integrated 10 k pull-up resistor to V_BCKP. Therefore an external pull-
up is not required on the application board.
Following are some typical examples of application circuits using the RESET_N input pin.
The simplest way to reset the module is to use a push button that shorts the RESET_N pin to ground.