# modbus_rtu_get_serial_mode(3) Manual Page

## NAME

modbus_rtu_get_serial_mode - get the current serial mode

## SYNOPSIS

int modbus_rtu_get_serial_mode(modbus_t *ctx);

## DESCRIPTION

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.

## RETURN VALUE

The modbus_rtu_get_serial_mode() 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.

## ERRORS

EINVAL

  The current libmodbus backend is not RTU.

## AUTHORS

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