User's Manual

SARA-R4 series - System Integration Manual
UBX-16029218 - R03 System description
Page 17 of 94
1.6 System function interfaces
1.6.1 Module power-on
When the SARA-R4 series modules are in the not-powered mode (i.e. the VCC module supply is not applied),
they can be switched on as follows:
 Rising edge on the VCC input pins to a valid voltage level, and then a low logic level has to be held at the
PWR_ON input pin for a valid time.
When the SARA-R4 series modules are in the power-off mode (i.e. switched off) or in the PSM low power mode,
with a valid VCC supply applied, they can be switched on as follows:
 Low pulse on the PWR_ON pin for a valid time period
The PWR_ON input pin is equipped with an internal active pull-up resistor. Detailed electrical characteristics with
voltages and timings are described in SARA-R4 series Data Sheet [1].
Figure 5 shows the module switch-on sequence from the not-powered mode, describing the following phases:
 The external power supply is applied to the VCC module pins
 The PWR_ON pin is held low for a valid time
 All the generic digital pins of the module are tri-stated until the switch-on of their supply source (V_INT).
 The internal reset signal is held low: the baseband core and all the digital pins are held in the reset state.
 When the internal reset signal is released, any digital pin is set in a proper sequence from the reset state to
the default operational configured state. The duration of this pins’ configuration phase differs within generic
digital interfaces and the USB interface due to host / device enumeration timings (see section 1.9.2).
 The module is fully ready to operate after all interfaces are configured.
VCC
PWR_ON
RESET_N
V_INT
Internal Reset
System State
BB Pads State
Internal Reset → Operational Operational
Tristate / Floating
Internal
Reset
OFF
ON
Start of interface
configuration
Module interfaces
are configured
Start-up
event
Figure 5: SARA-R4 series switch-on sequence description
The Internal Reset signal is not available on a module pin, but the host application can monitor the V_INT
pin to sense the start of the SARA-R4 series module switch-on sequence.
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 SARA-R4 series module is fully ready to operate, the host application processor should not
send any AT command over the AT communication interfaces (USB, UART) of the module.