LEON-G100 / LEON-G200 - System Integration Manual
GSM.G1-HW-09002-G3
Preliminary
System description
Page 56 of 125
1.9.2.2
DDC application circuit
General considerations
The DDC (I
2
C) interface of the LEON-G100 / LEON-G200 modules is used only to connect the wireless module to
a u-blox GPS receiver: the DDC (I
2
C) interface is enabled by the AT+UGPS command only (for more details refer
to
u-blox AT Commands Manual
[2]). The
SDA
and
SCL
lines must be connected to the DDC (I
2
C) interface pins
of the u-blox GPS receiver (i.e. the SDA2 and SCL2 pins of the u-blox GPS receiver) on the application board.
To be complaint with the I
2
C bus specifications, the module pads of the bus interface are open drain output and
pull-up resistors must be used. Since the pull-up resistors are not mounted on the module, they must be
mounted externally. Resistor values must conform to the I
2
C bus specifications [8]. If LEON-G100 / LEON-G200
modules are connected through the DDC bus to a u-blox GPS receiver (only one device can be connected on the
DDC bus), use a pull-up resistor of 4.7 k
. Pull-up resistors must be connected to a supply voltage of 2.85 V
(typical), since this is the voltage domain of the DDC pins (for detailed electrical characteristics see the
LEON-
G100 / LEON-G200 Data Sheet
DDC Slave-mode operation is not supported, the module can act as master only.
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. Since both lines are open drain outputs, the DDC devices can only drive them
low or leave them open. The pull-up resistor pulls the line up to the supply rail if no DDC device is pulling it
down to GND. If the pull-ups are missing,
SCL
and
SDA
lines are undefined and the DDC bus will not work.
The signal shape is defined by the values of the pull-up resistors and the bus capacitance. Long wires on the bus
will increase the capacitance. If the bus capacitance is increased, use pull-up resistors with nominal resistance
value lower than 4.7 k
, to match the
I
2
C bus specifications
[8] regarding rise and fall times of the signals.
Capacitance and series resistance must be limited on the bus to match the
I
2
C specifications
[8] (1.0 µs is
the maximum allowed rise time on the SCL and SDA lines): route connections as short as possible.
If the pins are not used as DDC bus interface, they can be left floating on the application board.
LEON-G100-06x / LEON-G200-06S and subsequent versions
LEON-G100-06x / LEON-G200-06S and subsequent versions support these GPS aiding types:
Local aiding
AssistNow Online
AssistNow Offline
AssistNow Autonomous
The embedded GPS aiding features can be used only if the DDC (I
2
C) interface of the wireless module is
connected to the u-blox GPS receivers.
The GPIO pins can handle:
The power on/off of the GPS receiver (“GPS supply enable” function provided by
GPIO2
)
The wake up from idle-mode when the GPS receiver is ready to send data (“GPS data ready” function
provided by
GPIO3
)
The RTC synchronization signal to the GPS receiver (“GPS RTC sharing” function provided by
GPIO4
)
GPIO2
is by default configured to provide the “GPS 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 GPS receiver connected
to the wireless module by the AT+UGPS command. The pin is set as
Output / High, to switch on the u-blox GPS receiver, if the parameter <mode> of AT+UGPS command is set
to 1
Output / Low, to switch off the u-blox GPS receiver, if the parameter <mode> of AT+UGPS command is set
to 0 (default setting)
