Specifications

LEON-G100/G200 - System Integration Manual
GSM.G1-HW-09002-C Preliminary System description
Page 48 of 75
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 [10]. If LEON-G100/G200 modules
are connected through the DDC bus to a single u-blox GPS receiver only (only one device is connected on the
DDC bus), use a pull-up resistor of 4.7 k . Pull-ups 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/G200
Data Sheet [1]).
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 lower nominal
resistance value than 4.7 k , to match the I
2
C bus specifications regarding rise and fall times of the signals [10].
Capacitance must be limited on the bus to match the I
2
C specifications: connections should be routed as
short as possible.
If the pins are not used as DDC bus interface, they can be left unconnected.
1.11.2.2 Minimal connections
The minimal connections are illustrated in the Figure 33.
Figure 33: DDC interface application circuit (connection with a GPS module)
1.12 ADC input (LEON-G100 only)
One Analog to Digital Converter input is available (ADC1) and is configurable using u-blox AT commands (see
u-blox AT Commands Manual [2]). The resolution of this converter is 12-bit with a single ended input range.
The electrical behavior of the measurement circuit in voltage mode can be modeled by a circuit equivalent to
that shown in Figure 34. This includes a resistor (R
eq
), voltage source (U
eq
), analog preamplifier (with typical gain
G=0.5), and a digital amplifier (with typical gain g
ADC
=2048 LSB/V).
LEON-G100/G200u-blox GPS receiver
SDA
SCL
31
30
SDA
SCL
4.7 k
4.7 k
2.85 V
2.85 V
LEON-G100/G200u-blox GPS receiver
SDA
SCL
31
30
SDA
SCL
4.7 k
4.7 k
2.85 V
2.85 V