SARA-G450 - System integration manual
UBX-18046432 - R08 System description Page 42 of 143
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1.9.3 Additional serial interface for FW upgrade and tracing (FT UART)
The additional UART interface for Firmware upgrade and tracing (FT UART) is a 3-wire unbalanced
asynchronous serial interface, supporting:
FW upgrades by means of the dedicated tool
Trace log capture (diagnostic purpose)
RF non-signaling test mode by means of dedicated commands
The main characteristics of the interface are the following:
Serial port with RS-232 functionality conforming to ITU-T V.24 recommendation [19] with CMOS
compatible signal levels: 0 V for low data bit or ON state and 1.8 V / 3 V for high data bit or OFF
state (for detailed electrical characteristics, see the SARA-G450 data sheet [1])
Data lines (RXD_FT as output, TXD_FT as input)
Software flow control (XON/XOFF)
Fixed baud-rate 921600 bit/s
Fixed frame format 8N1 (8 data bits, no parity, 1 stop bit)
☞ The signal names of the FT UART interface of SARA-G450 modules conform to the ITU-T V.24
recommendation [19]: e.g. the TXD_FT line represents the data transmitted by the DTE
(application processor data line output) and received by the DCE (module data line input).
☞ During the firmware upgrade procedure over the FT UART interface, the V_INT pin and the FT
UART interface operate at the level set by the flash programmer, regardless of the VSEL input pin
setting.
1.9.4 DDC (I2C) interface
☞ DDC (I2C) interface is not supported by the “00” product version. This interface should be left
unconnected and should not be driven by external devices.
SARA-G450 modules provide an I2C compatible DDC interface on the SCL and SDA pins exclusively
for the communication with u-blox GNSS positioning chips / modules.
The AT command interface is not available on the DDC (I2C) interface.
DDC (I2C) slave mode operation is not supported: the cellular module can act as master only, and the
connected u-blox GNSS receiver acts as slave in the DDC (I2C) communication.
Two lines, serial clock (SCL) and serial data (SDA), carry information on the bus. SCL is used to
synchronize data transfers, and SDA is the data line. To be compliant to the I2C bus specifications,
the module interface pins are open drain output and pull-up resistors must be externally provided
conforming to the I2C bus specifications [21].
u-blox has implemented special features in SARA-G450 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 (I2C) interface. A second interface connected to the positioning receiver
is not necessary: AT commands via the UART serial interface of the cellular module allow for full
control of the GNSS receiver from any host processor.
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