How to use UART RK3568

Overview

The Android/Linux UART/serial port access from user is through the tty-devices. The tty-devices have different names depending on UART driver on different board.

RS-485

RS-485 uses half-duplex communication, which means that one medium is shared for transmitting and receiving data.

Therefore the system needs to control the RS-485 transceiver's transmit mode.

Usually the UART RTS signal is used to switch the transmitter on and off.

Boards

RSB-4810 Borad

COM Name	Device Node	Remark
COM1	/dev/ttyS4	RS232 2-wire
COM2	/dev/ttyS7	RS232 2-wire
COM3	/dev/ttyUSB2	RS232 4-wire and RS485
COM4	/dev/ttyUSB3	RS232 4-wire and RS485
COM5	/dev/ttyUSB0	RS232 4-wire
COM6	/dev/ttyUSB1	RS232 4-wire

Note : 

 

KEDGE-350 Borad

Main Board

COM Name	Device Node	Remark
COM0	/dev/ttyS3	RS232 2-wire and RS485
COM1	/dev/ttyS4	RS232 2-wire and RS485
COM2(UIO)	/dev/ttyS7	RS232 2-wire
COM3(UIO)	/dev/ttyS8	RS232 2-wire

Note : 

1. Only COM0 and COM1 support RS485 mode.

 

UIO-4031

COM Name	Device Node	Remark
COM0	/dev/ttyUSB2	RS485
COM1	/dev/ttyUSB3	RS485
COM2	/dev/ttyUSB0	RS485
COM3	/dev/ttyUSB1	RS485
COM4	/dev/ttyS7	RS232 2-wire
COM5	/dev/ttyS8	RS232 2-wire

 

ROM-5880 Borad

COM Name	Device Node	Remark
COM1	/dev/ttyS3	RS232 4-wire
COM2	/dev/ttyS5	RS232 2-wire
COM3	/dev/ttyS4	RS232 4-wire
COM4	/dev/ttyS7	RS232 2-wire

Note : 

 

How to config RS232 or RS485 mode

Enter U-boot interrupt mode

Connect device to debug port, and open debug console. See more How_to_debug.

Press "ctrl + c" key before power up the device, until get the following information on debug console :

Hit any key to stop autoboot: 0
=> <INTERRUPT>
=>

Then you can input the following cammand to config UART mode.

Config Uart coming from cpu

RS485 Mode（Taking Kedge-350 for example）:

setenv uart_mode_cpu 3:1,4:1
saveenv
reset

RS232 Mode（Taking Kedge-350 for example）:

setenv uart_mode_cpu 3:0,4:0
saveenv
reset

Note :

The default value is RS485 for Kedge-350.

Above command "uart_mode_cpu 3:1,4:1", 3:1 means set ttyS3 to RS485(0 means to RS232; 1 means to RS485).

If you just want ttyS3(or ttyS4)to be RS485 mode, please change "3:1,4:1"to "3:1,4:0"(or "3:0,4:1").

Config Uart coming from cp2108

RS485 Mode:

setenv uart_mode 0x0c
saveenv
reset

RS232 Mode:

setenv uart_mode 0x00
saveenv
reset

Note :

The default value is RS232.

Cp210x support four port, but RSB4810 Only ttyUSB2 and ttyUSB3 support RS485 mode.

Above command "setenv uart_mode 0x0c", 0x0c means set bit2(ttyUSB2) and bit3(ttyUSB3) to 1 (0 means to RS232; 1 means to RS485).

If you just want ttyUSB2 (or ttyUSB3)to be RS485 mode, please change 0x0c to 0x04 (or 0x08).