UART¶

Introduction¶

Core-1684JD4 supports 3 UART devices:

Device name	Interface function	Baud rate	Full duplex	Level
/dev/ttyS0	Debug serial port	115200	yes	TTL
/dev/ttyS1	RS232	115200	yes	RS232
/dev/ttyS2	RS485	9600	No	RS485

The RS232 and RS485 interface diagram of Core-1684JD4 board is as follows:

_images/uart_interface.png

_images/uart_pinout.png

Debug¶

Users can use different host’s USB-to-serial adapters to send and receive data to the serial port of the development board according to different interfaces. For example, the debugging steps of RS485 are as follows:

(1) Connecting the hardware

Connect the A, B and GND pins of the RS485 of the development board to the A, B and GND pins of the host serial adapter (USB to 485 to serial port module) respectively.

(2) Open the serial terminal of the host

Open kermit in the terminal and set the baud rate:

$ sudo kermit
C-Kermit> set line /dev/ttyUSB0
C-Kermit> set speed 9600
C-Kermit> set flow-control none
C-Kermit> connect

/dev/ttyUSB0 is the device file of the USB-to-serial adapter

(3) Send data

The device file for RS485 is /dev/ttyS2. Run the following commands on the device:

sudo -s
stty -F /dev/ttyS2 9600 -echo
echo firefly RS485 test... > /dev/ttyS2

The serial terminal in the host can receive the string “firefly RS485 test…”

(4) Receive data

First run the following command on the device:

sudo -s
cat /dev/ttyS2

Then enter the string “Firefly RS485 test…” in the serial terminal of the host, and the same string can be seen on the device side.

How to restore RS232 to normal communication serial port function?¶

Open a terminal and enter the following command:

sudo systemctl disable --now serial-getty@ttyS1.service