Yunjin.jiang: Created page with " = '''Overview''' = The Android/Linux UART/serial port access from user is through the tty-devices. The tty-devices have different names depending on UA..."

2025-09-24T05:58:34Z

Created page with " = '''Overview''' = The Android/Linux UART/serial port access from user is through the tty-devices. The tty-devices have different names depending on UA..."

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= '''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''' =

== AOM-3841 Borad ==

{| border="1" cellpadding="1" cellspacing="1"
|-
| '''COM Name'''
| '''Device Node'''
| '''Remark'''
|-
| COM1
| /dev/ttyS2
| RS232 2-wire
|-
| COM2
| /dev/ttyS4
|
RS232 4-wire

RS485

|-
| M.2 E-Key
| /dev/ttyS6
| RS232 4-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 : [http://ess-wiki.advantech.com.tw/view/How_to_debug_RK3568 How_to_debug].

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

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

== Config Uart coming from cpu ==

'''RS485 Mode（Taking AOM-3841 for example）:'''
<pre>setenv uart_mode_cpu 4:1
saveenv
reset
</pre>

'''RS232 Mode（Taking AOM-3841 for example）:'''
<pre>setenv uart_mode_cpu 4:0
saveenv
reset
</pre>

'''Note :'''

The default value is RS232 for AOM-3841 ttyS4.

Above command "uart_mode_cpu 4:1", 4:1 means set ttyS4 to RS485(0 means to RS232; 1 means to RS485).

== Config Uart coming from cp2108 ==

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

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

'''Note : '''

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).

How to use UART RK3576 - Revision history

Yunjin.jiang: Created page with " = '''Overview''' = The Android/Linux UART/serial port access from user is through the tty-devices. The tty-devices have different names depending on UA..."