User's Manual

SARA-G3 and SARA-U2 series - System Integration Manual
UBX-13000995 - R18 Advance Information System description
Page 62 of 206
1.9.4 DDC (I
2
C) interface
SARA-G300 and SARA-G310 modules do not support DDC (I
2
C) interface.
An I
2
C bus compatible Display Data Channel (DDC) interface for communication with u-blox GNSS receivers is
available on SDA and SCL pins of SARA-G340, SARA-G350 and SARA-U2 modules. Only this interface provides
the communication between the u-blox cellular module and u-blox positioning chips and modules.
SARA-U2 modules additionally support the communication with other external I
2
C devices as an audio codec.
The AT commands interface is not available on the DDC (I
2
C) interface.
DDC (I
2
C) slave-mode operation is not supported: the cellular module can act as master only, and the connected
u-blox GNSS receiver or any other external I
2
C devices acts as slave in the DDC (I
2
C) communication.
Two lines, serial data (SDA) and serial clock (SCL), carry information on the bus. SCL is used to synchronize data
transfers, and SDA is the data line. To be compliant to the I
2
C bus specifications, the module interface pins are
open drain output and pull up resistors must be externally provided conforming to the I
2
C bus specifications [15].
u-blox has implemented special features in SARA-G340, SARA-G350 and SARA-U2 modules to ease the design
effort required for the integration of a u-blox cellular module with a u blox GNSS receiver.
Combining a u-blox cellular module with a u-blox GNSS receiver allows designers to have full access to the
positioning receiver directly via the cellular module: it relays control messages to the GNSS receiver via a
dedicated DDC (I
2
C) interface. A 2
nd
interface connected to the positioning receiver is not necessary: AT
commands via the UART or USB serial interface of the cellular module allows a fully control of the GNSS receiver
from any host processor.
SARA-G340, SARA-G350 and SARA-U2 modules feature embedded GNSS aiding that is a set of specific features
developed by u-blox to enhance GNSS performance, decreasing the Time To First Fix (TTFF), thus allowing to
calculate the position in a shorter time with higher accuracy.
SARA-G340, SARA-G350 and SARA-U2 modules support these GNSS aiding types:
x Local aiding
x AssistNow Online
x AssistNow Offline
x AssistNow Autonomous
The embedded GNSS aiding features can be used only if the DDC (I
2
C) interface of the cellular module is
connected to the u-blox GNSS receivers.
SARA-G340, SARA-G350 and SARA-U2 cellular modules provide additional custom functions over GPIO pins to
improve the integration with u-blox positioning chips and modules. GPIO pins can handle:
x GNSS receiver power-on/off: “GNSS supply enable” function provided by GPIO2 improves the positioning
receiver power consumption. When the GNSS functionality is not required, the positioning receiver can be
completely switched off by the cellular module that is controlled by AT commands
x The wake up from idle-mode when the GNSS receiver is ready to send data: “GNSS data ready” function
provided by GPIO3 improves the cellular module power consumption. 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 positioning receiver can wake up the cellular module if it is in idle-mode, so the cellular
module does not lose the data sent by the GNSS receiver even if power saving is enabled
x The RTC synchronization signal to the GNSS receiver: “GNSS RTC sharing” function provided by GPIO4
improves GNSS receiver performance, decreasing the Time To First Fix (TTFF), and thus allowing to calculate