Serial Usage

AIBOX-9075 has 2 RS485 serial.

The device node of RS485_1 is "/dev/ttyHS1"; and the device node of
RS485_2 is "/dev/ttyHS3".

Transmission Test

RS485 needs additional gpio to control send and receive.

   # export gpio no.695
   echo 695 > /sys/class/gpio/export

   # set direction as output
   echo out > /sys/class/gpio/gpio695/direction

   # echo 1 means gpio output high level, set RS485_1 to send mode
   echo 1 > /sys/class/gpio/gpio695/value

   # send the data
   echo "RS485_TEST" > /dev/ttyHS1

   # echo 0 means gpio output low level, set RS485_1 to receive mode
   echo 0 > /sys/class/gpio/gpio695/value

   # disable echo and start receiving
   stty -echo -F /dev/ttyHS1
   cat /dev/ttyHS1

   # operate RS485_2 with same method, but the control of RS485_2 is gpio no.693.