modbus_rtu_get_serial_mode - get the current serial mode

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

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

       The modbus_rtu_get_serial_mode() function shall return the serial mode currently used by the libmodbus
       context:

       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 available on Linux kernels 2.6.28 onwards and can only be used with a context using
       a RTU backend.

EINVAL
           The current libmodbus backend is not RTU.

       modbus_rtu_get_serial_mode - get the current serial mode

       The function shall return MODBUS_RTU_RS232 or MODBUS_RTU_RS485 if successful. Otherwise it shall return
       -1 and set errno to one of the values defined below.

intmodbus_rtu_get_serial_mode(modbus_t*ctx);