modbus_rtu_set_serial_mode - set the serial mode

       The libmodbus documentation was written by Stéphane Raimbault <stephane.raimbault@gmail.com>

libmodbus v3.1.6                                   12/09/2019                            MODBUS_RTU_SET_SERIA(3)

       The modbus_rtu_set_serial_mode() function shall set the selected serial mode:

       MODBUS_RTU_RS232
           the serial line is set for RS232 communication. RS-232 (Recommended Standard 232) is the traditional
           name for a series of standards for serial binary single-ended data and control signals connecting
           between a DTE (Data Terminal Equipment) and a DCE (Data Circuit-terminating Equipment). It is
           commonly used in computer serial ports

       MODBUS_RTU_RS485
           the serial line is set for RS485 communication. EIA-485, also known as TIA/EIA-485 or RS-485, is a
           standard defining the electrical characteristics of drivers and receivers for use in balanced digital
           multipoint systems. This standard is widely used for communications in industrial automation because
           it can be used effectively over long distances and in electrically noisy environments.

       This function is only supported on Linux kernels 2.6.28 onwards.

EINVAL
           The current libmodbus backend is not RTU.

       ENOTSUP
           The function is not supported on your platform.

       If the call to ioctl() fails, the error code of ioctl will be returned.

       modbus_rtu_set_serial_mode - set the serial mode

       The function shall return 0 if successful. Otherwise it shall return -1 and set errno to one of the
       values defined below.

intmodbus_rtu_set_serial_mode(modbus_t*ctx,intmode);