Installation Instructions

LISA-U2 series - System Integration Manual
UBX-13001118 - R19 Early Production Information System description
Page 86 of 175
The “GNSS 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 “GNSS 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 “GNSS 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 “GNSS 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 does not
send data by the DDC (I
2
C) interface, the module automatically enters idle-mode whenever possible. With the
“GNSS 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.
The GPIO4 is by default configured to provide the “GNSS RTC sharing” function (parameter <gpio_mode> of
+UGPIOC AT command set to 5), to provide an RTC (Real Time Clock) synchronization signal at the power up of
the u-blox GNSS receiver connected to the cellular module. The pin will be set as
 Output, to provide an RTC synchronization signal to the u-blox GNSS receiver for RTC sharing if the
parameter <mode> of AT+UGPS command is set to 1 and the parameter <GPS_IO_configuration> of
+UGPRF AT command is set to 32
 Output / Low, otherwise (default setting)
The pin that provides the “GNSS RTC sharing” function must be connected to the RTC synchronization signal of
the u-blox GNSS receiver (i.e. the pin EXTINT0 of the u-blox GNSS receiver) on the application board.
The “GNSS RTC sharing” function provides improved GNSS receiver performance, decreasing the Time To First
Fix (TTFF), and thus allowing to calculate the position in a shorter time with higher accuracy. When GPS local
aiding is enabled, the cellular module automatically uploads data such as position, time, ephemeris, almanac,
health and ionospheric parameter from the GNSS receiver into its local memory, and restores this to the GNSS
receiver at the next power up of the GNSS receiver.
Connection with u-blox 1.8 V GNSS receivers
Figure 47 shows an application circuit for connecting a LISA-U2 cellular module to a u-blox 1.8 V GNSS receiver.
 SDA and SCL pins of the LISA-U2 cellular module are directly connected to the relative I
2
C pins of the u-blox
1.8 V GNSS receiver, with appropriate pull-up resistors connected to the 1.8 V GNSS supply enabled after
the V_INT supply of the I
2
C pins of the LISA-U2 cellular module.
 GPIO3 and GPIO4 pins are directly connected respectively to the TxD1 and EXTINT0 pins of the u-blox
1.8 V GNSS receiver to provide “GNSS data ready” and “GNSS RTC sharing” functions.
 A pull-down resistor is mounted on GPIO4 line for correct “GNSS 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-U2 module is in the internal reset state.
 The V_BCKP supply output of the LISA-U2 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