User's Manual

SARA-R4 series - System Integration Manual
UBX-16029218 - R03 System description
Page 23 of 94
1.9 Data communication interfaces
SARA-R4 series modules provide the following serial communication interface:
 UART interface: Universal Asynchronous Receiver/Transmitter serial interface available for the communication
with a host application processor (AT commands, data communication, FW update by means of FOAT). See
section 1.9.1.
 USB interface: Universal Serial Bus 2.0 compliant interface available for the communication with a host
application processor (AT commands, data communication, FW update by means of the FOAT feature), for
FW update by means of the u-blox dedicated tool and for diagnostic. See section 1.9.2.
 DDC interface: I
2
C bus compatible interface available for the communication with u-blox GNSS positioning
chips or modules and with external I
2
C devices. See section 1.9.3.
1.9.1 UART interface
1.9.1.1 UART features
The UART interface is a 9-wire 1.8 V unbalanced asynchronous serial interface available on all the SARA-R4 series
modules, supporting:
 AT command mode
1
 Data mode and Online command mode
1
 Multiplexer protocol functionality
 FW upgrades by means of the FOAT feature (see 1.12.7)
The UART is available only if the USB is not enabled as AT command / data communication interface:
UART and USB cannot be concurrently used for this purpose.
UART interface provides RS-232 functionality conforming to the ITU-T V.24 Recommendation [5], with CMOS
compatible signal levels: 0 V for low data bit or ON state, and 1.8 V for high data bit or OFF state (for detailed
electrical characteristics see SARA-R4 series Data Sheet [1]), providing:
 data lines (RXD as output, TXD as input),
 hardware flow control lines (CTS as output, RTS as input),
 modem status and control lines (DTR as input, DSR as output, DCD as output, RI as output).
SARA-R4 series modules are designed to operate as cellular modems, i.e. as the data circuit-terminating
equipment (DCE) according to the ITU-T V.24 Recommendation [5]. A host application processor connected to
the module through the UART interface represents the data terminal equipment (DTE).
UART signal names of the cellular modules conform to the ITU-T V.24 Recommendation [5]: e.g. TXD line
represents data transmitted by the DTE (host processor output) and received by the DCE (module input).
SARA-R4 series modules’ UART interface is by default configured in AT command mode: the module waits for
AT command instructions and interprets all the characters received as commands to execute. All the
functionalities supported by SARA-R4 series modules can be in general set and configured by AT commands:
 AT commands according to 3GPP TS 27.007 [6], 3GPP TS 27.005 [7], 3GPP TS 27.010 [8]
 u-blox AT commands (for the complete list and syntax see the SARA-R4 series AT Commands Manual [2])
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For the definition of the interface data mode, command mode and online command mode see SARA-R4 series AT Commands Manual [1]