LISA-C2 series and FW75-C200 - System Integration Manual
UBX-13000620 - R21
Early Production Information
System description
Page 36 of 103
•
GNSS receiver power-on/off (“GPS supply enable” function provided by
GPIO2
)
•
The wake up from idle-mode when the GNSS receiver is ready to send data (“GPS data ready” function
provided by
GPIO3
)
The
GPIO2
is by default configured to provide the “GPS supply enable” function (parameter <gpio_mode> of
AT+UGPIOC command set to 3 by default), to enable or disable the supply of the u-blox GNSS receiver
connected to the cellular module by the AT+UGPS command. The pin is set as
•
Output / High, to switch on the u-blox GNSS receiver, if the parameter <mode> of AT+UGPS command is
set to 1
•
Output / Low, to switch off the u-blox GNSS receiver, if the parameter <mode> of AT+UGPS command is set
to 0 (default setting)
The pin must be connected to the active-high enable pin (or the active-low shutdown pin) of the voltage
regulator that supplies the u-blox GNSS receiver on the application board.
The “GPS supply enable” function improves the power consumption of the GNSS receiver. When the GNSS
functionality is not required, the GNSS receiver can be completely switched off by the cellular module that is
controlled by the application processor with AT commands.
The
GPIO3
is by default configured to provide the “GPS data ready” function (parameter <gpio_mode> of
AT+UGPIOC command set to 4 by default), to sense when the u-blox GNSS receiver connected to the cellular
module is ready to send data by the DDC (I
2
C) interface. The pin will be set as:
•
Input, to sense the line status, waking up the cellular module from idle-mode when the u-blox GNSS receiver
is ready to send data by the DDC (I
2
C) interface, if the parameter <mode> of +UGPS AT command is set to 1
and the parameter <GPS_IO_configuration> of +UGPRF AT command is set to 16
•
Tri-state with an internal active pull-down enabled, otherwise (default setting)
The pin that provides the “GPS data ready” function must be connected to the data ready output of the u-blox
GNSS receiver (i.e. the pin TxD1 of the u-blox GNSS receiver) on the application board.
The “GPS data ready” function provides an improvement in the power consumption of the cellular module.
When power saving is enabled in the cellular module by the AT+UPSV command and the GNSS receiver doesn’t
send data by the DDC (I
2
C) interface, the module automatically enters idle-mode whenever possible. With the
“GPS data ready” function the GNSS receiver can indicate to the cellular module that it is ready to send data by
the DDC (I
2
C) interface: the GNSS receiver can wake up the cellular module if it is in idle-mode, so that data sent
by the GNSS receiver will not be lost by the cellular module even if power saving is enabled.
Figure 19 illustrates the application circuit for connecting a LISA-C cellular module to a u-blox GNSS 1.8 V
receiver.
SDA
and
SCL
pins of the LISA-C cellular module are directly connected to the relative pins of the u-blox GNSS
1.8 V
receiver, with appropriate pull-up resistors.
GPIO3
is directly connected respectively to the
TxD1
pin of the u-blox GNSS 1.8 V
receiver to provide “GPS data
ready” functionality, and
GPIO4
is directly connected to the
EXTINT0
pin of the GNSS receiver to provide RTC
synchronization timing input.
A pull-down resistor is mounted on the
GPIO4
line for correct “GPS RTC sharing” function implementation.
A pull-down resistor is mounted on the
GPIO2
line to avoid a switch on of the u-blox GNSS receiver when the
LISA-C module is in the internal reset state.
The
V_BCKP
supply output of the u-blox cellular module is connected to the
V_BCKP
backup supply input pin of
the GNSS receiver to provide the supply for the GNSS real time clock and backup RAM when the
VCC
supply of
the cellular module is within its operating range and the
VCC
supply of the GNSS receiver is disabled. This
enables the u-blox GNSS receiver to recover from a power breakdown with either a hot start or a warm start
(depending on the duration of the GNSS
VCC
outage) and to maintain the configuration settings saved in the
backup RAM.
