Integration Manual

LISA-U2 series - System Integration Manual
UBX-13001118 - R25 System description Page 86 of 182
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 the 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 levels could be required if the lines are externally accessible on the application
board. Higher protection levels can be achieved by mounting an ESD protection (e.g. EPCOS
CA05P4S14THSG varistor array) on the lines connected to these pins, close to the 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 full 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 interval 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 the GNSS Implementation Application Note [15].
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: besides the general
considerations reported below, see section 1.10.2.2 for specific guidelines and application circuit
examples for the connection to u-blox GNSS receivers and see section 1.11 for an application circuit
example with an external audio codec I
2
C-bus slave.
To be compliant with the I
2
C bus specifications, the module bus interface pads are open drain output
and pull up resistors must be mounted externally. Resistor values must conform to the I
2
C bus