u-blox LEON-G100 ECALL, System Integration Manual

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LEON-G100 / LEON-G200 - System Integration Manual
GSM.G1-HW-09002-G3 Preliminary System description
Page 37 of 125
1.6.3 Module reset
LEON-G100 / LEON-G200 modules can be reset using the RESET_N pin: when the RESET_N pin is forced low
for at least 50 ms, an “external” or “hardware” reset is performed, that causes an asynchronous reset of the
entire module, except for the RTC. Forcing an “external” or “hardware” reset, the current parameter settings
are not saved in the module’s non-volatile memory and a proper network detach is not performed.
LEON-G100 / LEON-G200 modules can also be reset by means of the AT command AT+CFUN (more details in
u-blox AT Commands Manual [2]): in this case an “internal” or “software” reset is performed, that causes, like
the “external” or “hardware” reset, an asynchronous reset of the entire module except for the RTC. Forcing an
“internal” or “software” reset, the current parameter settings are saved in the module’s non-volatile memory
and a proper network detach is performed.
The
RESET_N pin is pulled low by the module when the module is in power-off mode or an internal reset
occurs. In these cases an internal open drain FET pulls the line low.
Name Description Remarks
RESET_N Reset signal A series Schottky diode is integrated in the module as protection.
An internal 12.6 k
Ω pull-up resistor pulls the line to 1.88 V when
the module is not in the reset state. An internal open drain FET
pulls the line low when an internal reset occurs and when the
module is in power down mode.
Table 12: Reset pin
RESET_N pin ESD sensitivity rating is 1 kV (HBM JESD22-A114F). A higher protection level could be
required if the line is externally accessible on the application board. A higher protection level can be
achieved mounting an ESD protection (e.g. EPCOS CA05P4S14THSG varistor array) on the line
connected to this pin if it is externally accessible on the application board.
For more details about the general precautions for ESD immunity about RESET_N pin, refer to chapter
2.5.1.
The reset state of each digital pin is reported in the pin description table in the
LEON-G100 / LEON-G200 Data
Sheet [1].
The electrical characteristics of
RESET_N are different from the other digital I/O interfaces. The high and low
logic levels have different operating ranges and absolute maximum ratings. The detailed electrical characteristics
are described in the
LEON-G100 / LEON-G200 Data Sheet [1].
As described in the Figure 21, a series Schottky diode is mounted inside the module on the RESET_N pin to
increase the maximum allowed input voltage up to 4.5 V as operating range. Nevertheless the module senses a
low level when the
RESET_N pin is forced low from the external.
As described in Figure 21, the module has an internal pull-up resistor (12.6 k Ω typical) which pulls the level on
the
RESET_N
pin to 1.88 V (typical) when the module is not in reset state. Therefore an external pull-up is not
required on the application board.
Forcing
RESET_N low for at least 50 ms will cause an external reset of the module. When RESET_N is released
from the low level, the module automatically starts its power-on reset sequence.
If
RESET_N
is connected to an external device (e.g. an application processor on an application board) an open
drain output can be directly connected without any external pull-up. Otherwise, use a push-pull output. Make
sure to fix the proper level on
RESET_N
in all possible scenarios, to avoid unwanted reset of the module.
As an ESD immunity test precaution, a 47 pF bypass capacitor (e.g. Murata GRM1555C1H470JA01) and a series
ferrite bead (e.g. Murata BLM15HD182SN1) must be added on the
RESET_N line pin to avoid a module reset
caused by an electrostatic discharge applied to the application board (for more details, refer to chapter 2.5.1).