LISA-U2 series - System Integration Manual
UBX-13001118 - R19
Early Production Information
System description
Page 84 of 175
1.10
DDC (I
2
C) interface
1.10.1
Overview
An I
2
C bus compatible Display Data Channel (DDC) interface for communication with u-blox GNSS receivers is
available on LISA-U2 modules. The communication between a u-blox cellular module and a u-blox GNSS receiver
is only provided by this DDC (I
2
C) interface.
Name
Description
Remarks
SCL
I
2
C bus clock line
Open drain. External pull-up required.
SDA
I
2
C bus data line
Open drain. External pull-up required.
Table 37: DDC pins
The DDC (I
2
C) interface pins ESD sensitivity rating is 1 kV (HBM according to JESD22-A114F). Higher
protection level could be required if the lines are externally accessible on the application board. Higher
protection level can be achieved by mounting an ESD protection (e.g. EPCOS CA05P4S14THSG varistor
array) on the lines connected to these pins, close to accessible points.
u-blox has implemented special features in LISA-U2 series cellular 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 GNSS
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 GNSS receiver is not necessary: AT commands via the serial interfaces
(UART, USB, SPI) of the cellular module allows a fully control of the GNSS receiver from any host processor.
LISA-U2 modules feature embedded GPS aiding that is a set of specific features developed by u-blox to enhance
GNSS performance, decreasing Time To First Fix (TTFF), thus allowing to calculate the position in a shorter time
with higher accuracy.
The DDC (I
2
C) interface of all LISA-U2 series modules can be used to communicate with u-blox GNSS receivers
and with external I
2
C devices as an audio codec: the cellular module acts as an I
2
C master which can
communicate to more I
2
C slaves as allowed by the
I
2
C bus specifications
[8]. See section 1.11 for an application
circuit with an external audio codec.
For more details regarding the handling of the DDC (I
2
C) interface and the GPS aiding features, see the
u-blox AT Commands Manual
[2] (AT+UGPS, AT+UGPRF, AT+UGPIOC, +UI2CO, +UI2CW, +UI2CR,
+UI2CREGR, +UI2CC AT commands) and
GNSS Implementation Application Note
1.10.2
DDC application circuits
1.10.2.1
General considerations
The DDC I
2
C-bus master interface of LISA-U2 series modules can be used to communicate with u-blox GNSS
receivers and with other external I
2
C-bus slaves as an audio codec: beside the general considerations reported
below, see the section 1.10.2.2 for specific guidelines and application circuit examples for the connection to u-
blox GNSS receivers and see the section 1.11 for an application circuit example with an external audio codec I
2
C-
bus slave.
