UART

Introduction

ITX-3568Q supports UART、RS232、RS485 interfaces

UARTx1

RS485x1

RS232x1

The RS232 of the board is extended from RK3568 uart3, RS485 is
extended from uart0 and UART is uart9.

DTS configuration

File "kernel/arch/arm64/boot/dts/rockchip/rk3568-firefly-itx-
3568q.dtsi" has the definition of spi to uart related nodes:

   &uart3 {
   	pinctrl-names = "default";
   	pinctrl-0 = <&uart3m0_xfer>;
       status = "okay";
   };

   &uart0 {
       status = "okay";
   };

   &uart9 {
   	pinctrl-names = "default";
   	pinctrl-0 = <&uart9m1_xfer>;
       status = "okay";
   };

After the serial port is configured, the nodes on the hardware
interface corresponding to the software are:

   RS485:   /dev/ttyS0
   UART9:   /dev/ttyS9
   RS232:   /dev/ttyS3

PINs Definition

RS232 & RK485

UART9

RS232/RS485 Instruction

The following commands can be used to switch RS485/RS232:

Android

   echo 255 > /sys/class/leds/firefly\:rs232_485_switch\:user/brightness  //enabled RS485
   echo 0 > /sys/class/leds/firefly\:rs232_485_switch\:user/brightness  //enabled RS232

Linux

   uart-switch.sh on  //enable RS485
   uart-switch.sh off  //enable RS232
   uart-switch.sh status  //current status

Debug method

Users can send and receive data to the serial port of the development
board by using the USB to serial port adapter of different host
according to different interfaces. For example, the debugging steps of
RS485 are as follows:

(1) Connected hardware

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

(2) Open the serial terminal of the host

Input the install Kermit command "sudo apt install Kermit" on the
terminal. After the installation, open Kermit, set the baud rate and
connect:

   $ 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 for USB to serial port adapter.

(3) Send data to host serial port adapter

The device file for RS485 is "/dev/ttyS0". Run the following commands
on the device:

   echo firefly RS485 test... > /dev/ttyS0

The serial terminal in the host can receive a string: "firefly RS485
test... "

(4) Receive data from host serial port adapter

First run the following commands on the device:

   cat /dev/ttyS0

Then enter a string at the host's serial terminal: "Firefly RS485
test...", the device side can see the same string.

(5) Exit kermit connection

The host hit keyboard "ctrl+\" and then hit key c, input "exit" and
hit enter

   C-Kermit>exit
   OK to exit? ok