User Guide

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3.4 UART Interface
Table 6 lists the UART interface signals.
Table 6 UART interface signals
Pin No. Pin name I/O
Typ.(V) Description
23 UART_RXD DI 1.8V Receive data
31 UART_TXD DO 1.8V Send data
28 UART_CTS DI 1.8V Clear to Send
25 UART_RTS DO 1.8V Ready for Receive
The M3B module is available with 1-wire hardware flow control UART (DSR and R1 signal are not
supported), which supports 9600, 19200, 38400, 57600, 115200, 230400bps and the default value is
115200bps.
Figure 4 shows the recommended power circuit of level match in the 3.3V power. Pay attention
to the connection direction. The dotted circuit and full circuit can be used as reference to each other.
Figure 4 Recommended Power Circuit of Level Match
MCU/ARM
/TXD
/RXD
VDD_EXT
10 K
VCC_MCU
4.7 K
K 10
VDD_EXT
UART_TXD
UART_RXD
UART_RTS
UART_CTS
/RTS
/CTS
GND
Module
VDD_EXT
4.7 K
GND
1 nF
1 nF
Voltage level: 3.3V
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uCloudlink M3B Mini PCIe-C _Hardware Design Guide_V1.0