View source for How to use UART for RK3399 RSB4710


= '''Overview''' =

<font color="#000000">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.</font>

== <font color="#0066cc">RS-485</font> ==

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 ==

{| border="1" cellpadding="1" cellspacing="1"
|-
| '''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&nbsp;:&nbsp;'''

1. Only COM4、USB2COM0、USB2COM1、USB2COM2、USB2COM3&nbsp;are designed for custom using.

2. Only USB2COM2 and&nbsp;USB2COM3&nbsp;support RSB485.

3. COM2 is designed as debug port default.&nbsp;

= How to config RS232 or RS485 mode =

Enter U-boot interrupt mode

Connect device to debug port, and open debug console. See more&nbsp;:&nbsp;[http://ess-wiki.advantech.com.tw/view/How_to_debug_for_RK3399_RSB4710 How_to_debug].

Press&nbsp;"ctrl + c" key before power up the device, until get the following information on debug console&nbsp;:&nbsp;
<pre>Hit any key to stop autoboot: 0
=> <INTERRUPT>
=></pre>

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

== Config Uart Mode ==

Only ttyUSB2 and ttyUSB3 support RS485 mode.

'''RS485 Mode:&nbsp;'''
<pre>setenv uart_mode 0x0c
saveenv
reset
</pre>

'''RS232&nbsp;Mode:&nbsp;'''
<pre>setenv uart_mode 0x00
saveenv
reset
</pre>

'''RS422&nbsp;Mode: (ADS-B3399G)'''
<pre>setenv uart_mode 0xf
saveenv
reset
</pre>

'''Note&nbsp;:&nbsp;'''

The default value is RS232.&nbsp;

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).