SARA-G3 and SARA-U2 series - System Integration Manual
UBX-13000995 - R26
System description
Page 66 of 217
1.9.3.2
USB and power saving
The modules automatically enter the USB suspended state when the device has observed no bus traffic for a
specific time period according to the
USB 2.0 specifications
[14]. In suspended state, the module maintains any
USB internal status as device. In addition, the module enters the suspended state when the hub port it is
attached to is disabled. This is referred to as a USB selective suspend.
If the USB is suspended and a power saving configuration is enabled by the AT+UPSV command, the module
automatically enters the low power idle mode whenever possible but it wakes up to active mode according to
any required activity related to the network (e.g. the periodic paging reception described in section 1.5.1.4) or
any other required activity related to the functions / interfaces of the module.
The module exits suspend mode when there is bus activity. If the USB is connected and not suspended, the
module is forced to stay in active mode, therefore the AT+UPSV settings are overruled but they have effect on
the power saving configuration of the other interfaces.
The modules are capable of USB remote wake-up signaling: i.e. it may request the host to exit suspend mode or
selective suspend by using electrical signaling to indicate remote wake-up, for example due to incoming call,
URCs, data reception on a socket. The remote wake-up signaling notifies the host that it should resume from its
suspended mode, if necessary, and service the external event. Remote wake-up is accomplished using electrical
signaling described in the
USB 2.0 specifications
For the module current consumption description with power saving enabled and USB suspended, or with power
saving disabled and USB not suspended, see sections 1.5.1.4, 1.5.1.5 and the
SARA-U2 series Data Sheet
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
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 kaming it
possible to calculate the position in a shorter time with higher accuracy.
