Uart Interfaces - Quectel EC25-AUX Hardware Design

A common mode choke L1 is recommended to be added in series between the module and customer's
MCU in order to suppress EMI spurious transmission. Meanwhile, the 0Ω resistors (R3 and R4) should be
added in series between the module and the test points so as to facilitate debugging, and the resistors are
not mounted by default. In order to ensure the integrity of USB data line signal, L1/R3/R4 components
must be placed close to the module, and also these resistors should be placed close to each other. The
extra stubs of trace must be as short as possible.
The following principles should be complied with when design the USB interface, so as to meet USB 2.0
specification.
 It is important to route the USB signal traces as differential pairs with total grounding. The impedance
of USB differential trace is 90Ω.
 Do not route signal traces under crystals, oscillators, magnetic devices and RF signal traces. It is
important to route the USB differential traces in inner-layer with ground shielding on not only upper
and lower layers but also right and left sides.
 Pay attention to the influence of junction capacitance of ESD protection components on USB data
lines. Typically, the capacitance value should be less than 2.0pF.
 Keep the ESD protection components to the USB connector as close as possible.

3.11. UART Interfaces

The module provides two UART interfaces: the main UART interface and the debug UART interface. The
following shows their features.
 The main UART interface supports 4800bps, 9600bps, 19200bps, 38400bps, 57600bps, 115200bps,
230400bps, 460800bps and 921600bps baud rates, and the default is 115200bps. This interface is
used for data transmission and AT command communication.
The debug UART interface supports 115200bps baud rate. It is used for Linux console and log

output.
The following tables show the pin definition of the UART interfaces.
Table 11: Pin Definition of Main UART Interface
Pin Name Pin No.
RI 62
DCD 63
CTS 64
EC25_Hardware_Design
I/O Description
DO Ring indicator
DO Data carrier detection
DO Clear to send
LTE Standard Module Series
EC25 Hardware Design
Comment
1.8V power domain
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