SARA-R4 series - System Integration Manual
UBX-16029218 - R06
System description
Page 24 of 102
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, 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, 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.
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 series
modules, supporting:
AT command mode
2
Data mode and Online command mode2
Multiplexer protocol functionality
FW upgrades by means of the FOAT feature (see 1.13.7)
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
[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).
Hardware flow control is not supported by “00”, “01” and “02” product versions, but the
RTS
input line
of the module has to be set low (= ON state) to communicate over UART interface.
DTR
input of the module has to be set low (= ON state) to have URCs presented over UART interface.
2
For the definition of the interface data mode, command mode and online command mode see
SARA-R4 series
AT Commands Manual
