RSB-3730 UART（RS-232/RS-485）

UART

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

How to Config RS232 or RS485 Mode

COM Name	Device Node	Remark
UIO2 com1	/dev/ttymxc0	support RS232
COM1/DEBUG2	/dev/ttymxc1	Debug Port
COM	/dev/ttymxc2	support RS232/RS485
UIO2 com4	/dev/ttymxc3	support RS232

Enter U-boot interrupt mode  Connect device to debug port, and open debug console.
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.

RS485 Mode：

=> setenv uart_mode 2:1
=> saveenv
=> reset

RS232 Mode：

=> setenv uart_mode 2:0
=> saveenv
=> reset

Note：The default value is RS232.

The above command "setenv uart_mode 2:1", 2:1 means to set ttymxc2 to RS485 standard mode, and 2:0 means to set ttymxc2 to RS232 mode.
The following RS232 testing method is shared by "/dev/ttymxc0, /dev/ttymxc2, /dev/ ttymxc3",and only needs to be replaced Uart Name.

RS232- Loopback Test

# stty -F /dev/ttymxc0 -echo -onlcr 115200
# cat /dev/ttymxc0 &
# echo "Serial Port Test" > /dev/ttymxc0

RS-485 Test

Test RS-485 with Adam-4520I. Connect Adam-4520I to PC with DB9 cable.Connect Adam-4520I to COMX DB9.

# stty -F /dev/ttymxc2 speed 115200 ignbrk -brkint \
-icrnl -imaxbel -opost -onlcr -isig -icanon \
-iexten -echo -echoe -echok -echoctl -echoke
# cat /dev/ttymxc2 &
# echo test > /dev/ttymxc2

Receive “test” on PC terminal.