MikroTik router board M33G have 3 serial interfaces: one RS232 on via standard 9-pin D-sub connector and two on the pin-header on the board.
My intention is to use second serial interface on the board via pin-head to UART - RS485 convertor for communication with other devices via Modbus RTU.
My problem is when I trying communicate via ttyS1 with libmodbus library, I've got: I/O error.
Communication via ttyS0 is without errors.
Is there some missing UART driver for ttyS1 and ttyS2 in OpenWrt or where can by problem?