Integration Manual

LISA-U2 series - System Integration Manual
UBX-13001118 - R25 System description Page 88 of 182
The GPIO2 is configured by default to provide the “GNSS 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 “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 the calculation of 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 parameters from the GNSS
receiver into its local memory, and restores this to the GNSS receiver at the next power-up of the
GNSS receiver.