# modbus_new_rtu(3) Manual Page

## NAME

modbus_new_rtu - create a libmodbus context for RTU

## SYNOPSIS

modbus_t *modbus_new_rtu(const char *device, int baud, char parity, int data_bit, int stop_bit);

## DESCRIPTION

The modbus_new_rtu() function shall allocate and initialize a modbus_t structure to communicate in RTU mode on a serial line.

The device argument specifies the name of the serial port handled by the OS, eg. /dev/ttyS0 or /dev/ttyUSB0. On Windows, it’s necessary to prepend COM name with \\.\ for COM number greater than 9, eg. \\\\.\\COM10. See http://msdn.microsoft.com/en-us/library/aa365247(v=vs.85).aspx for details

The baud argument specifies the baud rate of the communication, eg. 9600, 19200, 57600, 115200, etc.

The parity argument can have one of the following values

  - N for none

  - E for even

  - O for odd

The data_bits argument specifies the number of bits of data, the allowed values are 5, 6, 7 and 8.

The stop_bits argument specifies the bits of stop, the allowed values are 1 and 2.

## RETURN VALUE

The modbus_new_rtu() function shall return a pointer to a modbus_t structure if successful. Otherwise it shall return NULL and set errno to one of the values defined below.

## ERRORS

EINVAL

  An invalid argument was given.

## EXAMPLE

    modbus_t *ctx;

    ctx = modbus_new_rtu("/dev/ttyUSB0", 115200, 'N', 8, 1);
    if (ctx == NULL) {
        fprintf(stderr, "Unable to create the libmodbus context\n");
        return -1;
    }

## SEE ALSO

modbus_new_tcp(3) modbus_free(3)

## AUTHORS

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