Integration Manual
SARA-R4/N4 series - System Integration Manual
UBX-16029218 - R13 System description Page 29 of 119
1.9 Data communication interfaces
SARA-R4/N4 series modules provide the following serial communication interface:
• USB interface: Universal Serial Bus 2.0 compliant interface available for the communication with a host application
processor (AT commands, data, FW update by means of the FOAT feature), for FW update by means of the u-blox
dedicated tool and for diagnostics. See section 1.9.2.
• SPI interface: Serial Peripheral Interface available for communication with an external compatible device. See section
1.9.3.
• SDIO interface: Secure Digital Input Output interface available for communication with a compatible device. See
section 1.9.4.
• 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 1.9.5.
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/N4 series
modules, supporting:
• AT command mode
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• Data mode and Online command mode
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• Multiplexer protocol functionality
• FW upgrades by means of the FOAT feature (see 1.13.7)
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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 electrical characteristics see the
SARA-R4/N4 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/N4 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 UART
interface represents the data terminal equipment (DTE).
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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).
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Hardware flow control is not supported by the “00”, “01” and the SARA-R410M-02B-00 product versions, but the RTS
input line of the module must be set low (= ON state) to communicate over UART interface on the “00” and “01”
product versions.
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DTR input of the module must be set low (= ON state) to have URCs presented over UART interface.
SARA-R4/N4 series modules’ UART interface is by default configured in AT command mode, if the USB interface is not
enabled as AT command / data communication interface (UART and USB cannot be concurrently used for this purpose):
the module waits for AT command instructions and interprets all the characters received as commands to execute. All
the functionalities supported by SARA-R4/N4 series modules can be in general set and configured by AT commands:
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For the definition of the interface data mode, command mode and online command mode see SARA-R4/N4 series AT Commands Manual [1]