How to use UART for RK3399 RSB4710
Contents
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
RSB4710 Borad
| COM Name | Device Node | Remark |
| COM0 | /dev/ttyS0 | pull to M2 interface for BT using |
| COM1 | /dev/ttyS4 | support RS232, no flow control |
| COM2 | /dev/ttyS2 | Debug Port |
| COM3 | /dev/ttyUSB0 | support RS232 |
| COM4 | /dev/ttyUSB1 | support RS232 |
| COM5 | /dev/ttyUSB2 | support RS232 and RS485 |
| COM6 | /dev/ttyUSB3 | support RS232 and RS485 |
Note :
1. Only COM4、USB2COM0、USB2COM1、USB2COM2、USB2COM3 are designed for custom using.
2. Only USB2COM2 and USB2COM3 support RSB485.
3. COM2 is designed as debug port default.
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 Mode
Only ttyUSB2 and ttyUSB3 support RS485 mode.
RS485 Mode:
setenv uart_mode 0x0c saveenv reset
RS232 Mode:
setenv uart_mode 0x00 saveenv reset
RS422 Mode: (ADS-B3399G)
setenv uart_mode 0xf saveenv reset
Note :
The default value is RS232.
Cp210x support four port, but RSB4710 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 RSB485 mode, please change 0x0c to 0x04 (or 0x08).