# modbus_rtu_set_serial_mode(3) Manual Page

## NAME

modbus_rtu_set_serial_mode - set the serial mode

## SYNOPSIS

int modbus_rtu_set_serial_mode(modbus_t *ctx);

## DESCRIPTION

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.

## RETURN VALUE

The modbus_set_serial_mode() function shall return 0 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.

ENOTSUP

  The function is not supported on your platform.

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

## AUTHORS

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