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The configuration and behavior of the UART signals after the boot sequence are described below:
•
The module data output line (RXD) is set by default to the OFF state (high level) at UART
initialization. The module holds RXD in the OFF state until the module transmits some data.
•
The module data input line (TXD) is assumed to be controlled by the external host once UART is
initialized. The TXD data input line has an internal active pull-up enabled.
1.9.1.3
UART multiplexer protocol
LEXI-R422 modules include multiplexer functionality as per 3GPP TS 27.010 [8], on the primary UART
physical link. This is a data link protocol which uses HDLC-like framing and operates between the
module (DCE) and the application processor (DTE) and allows a number of simultaneous sessions over
the primary UART physical link. The following virtual channels are defined:
•
Channel 0: for multiplexer control.
•
Channel 1: for all AT commands, and non-Dial Up Network (non-DUN) data connections. UDP,
TCP data socket / data call connections via relevant AT commands.
•
Channel 2: for Dial Up Network (DUN) data connection. It requires the host to have and use its
own TCP/IP stack. The DUN can be initiated on modem side or terminal/host side.
•
Channel 3: for u-blox GNSS data tunneling.
1.9.2
USB interface
1.9.2.1
USB features
LEXI-R422 modules include a high-speed USB 2.0 interface [4], available for FW upgrade by means of
the u-blox EasyFlash tool and for diagnostic purposes. The module itself acts as a USB device, and it
can be connected to a USB host such as a Personal Computer equipped with compatible drivers.
LEXI-R422 modules provide the following USB lines:
•
the USB_D+ / USB_D- lines, carrying the USB data and signaling
•
the USB_5V0 input pin to enable the USB interface by applying an external 5.0 V typical voltage
•
the USB_3V3 input pin to supply the USB interface by applying an external 3.3 V typical voltage
☞
If the USB interface is enabled, the module does not enter the low power deep-sleep mode.
☞
It is highly recommended to provide accessible test points directly connected to the V_INT,
PWR_CTRL, USB_5V0, USB_3V3, USB_D+, USB_D-, RSVD #99 pins for FW upgrade and/or for
diagnostic purpose.
1.9.3
I2C interface
LEXI-R422 modules include an I2C-bus compatible interface (SDA, SCL lines) to communicate with
an external u-blox GNSS receiver and with external I2C devices: the LEXI-R422 module acts as an I2C
host which can communicate with I2C devices in accordance with the I2C bus specifications [9].
The SDA and SCL pins have internal pull-up to V_INT, so there is no need of additional pull-up resistors
on the external application board.
UBX-23007449 - R02
C1-Public
LEXI-R422 - System integration manual
System description
Page 29 of 108
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