libmodbus/doc/modbus_set_slave.txt

modbus_set_slave(3)
===================


NAME
----
modbus_set_slave - set slave number in the context


SYNOPSIS
--------
*int modbus_set_slave(modbus_t *'ctx', int 'slave');*


DESCRIPTION
-----------
The _modbus_set_slave()_ function shall set the slave number in the libmodbus
context.

The behavior depends of network and the role of the device:

*RTU*::
Define the slave ID of the remote device to talk in master mode or set the
internal slave ID in slave mode. According to the protocol, a Modbus device must
only accept message holing its slave number or the special broadcast number.

*TCP*::
The slave number is only required in TCP if the message must reach a device
on a serial network. The special value 'MODBUS_TCP_SLAVE' (0xFF) can be used in TCP mode to restore
the default value.

The broadcast address is 'MODBUS_BROADCAST_ADDRESS'. This special value must be
use when you want all Modbus devices of the network receive the request.


RETURN VALUE
------------
The _modbus_set_slave()_ function shall return 0 if successful. Otherwise it
shall return -1 and set errno to one of the values defined below.


ERRORS
------
*EINVAL*::
The slave number is invalid.


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