modbus_new_rtu(3)
=================


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.

Once the _modbus_t_ structure is initialized, you must set the slave of your
device with linkmb:modbus_set_slave[3] and connect to the serial bus with
linkmb:modbus_connect[3].

RETURN VALUE
------------
The 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.

*ENOMEM*::
Out of memory. Possibly, the application hits its memory limit and/or whole
system is running out of memory.


EXAMPLE
-------
[source,c]
-------------------
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;
}

modbus_set_slave(ctx, YOUR_DEVICE_ID);

if (modbus_connect(ctx) == -1) {
    fprintf(stderr, "Connection failed: %s\n", modbus_strerror(errno));
    modbus_free(ctx);
    return -1;
}
-------------------

SEE ALSO
--------
linkmb:modbus_new_tcp[3]
linkmb:modbus_free[3]


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