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LIBMODBUS(7)		       libmodbus Manual			  LIBMODBUS(7)

NAME
       libmodbus - a fast and portable Modbus library

SYNOPSIS
       #include	<modbus.h>

       cc `pkg-config --cflags --libs libmodbus` files

DESCRIPTION
       libmodbus is a library to send/receive data with	a device which
       respects	the Modbus protocol. This library contains various backends to
       communicate over	different networks (eg.	serial in RTU mode or Ethernet
       in TCP/IPv6). The http://www.modbus.org site provides documentation
       about the protocol at http://www.modbus.org/specs.php.

       libmodbus provides an abstraction of the	lower communication layers and
       offers the same API on all supported platforms.

       This documentation presents an overview of libmodbus concepts,
       describes how libmodbus abstracts Modbus	communication with different
       hardware	and platforms and provides a reference manual for the
       functions provided by the libmodbus library.

   Contexts
       The Modbus protocol contains many variants (eg. serial RTU or Ehternet
       TCP), to	ease the implementation	of a variant, the library was designed
       to use a	backend	for each variant. The backends are also	a convenient
       way to fulfill other requirements (eg. real-time	operations). Each
       backend offers a	specific function to create a new modbus_t context.
       The modbus_t context is an opaque structure containing all necessary
       information to establish	a connection with others Modbus	devices
       according to the	selected variant.

       You can choose the best context for your	needs among:

       RTU Context
	   The RTU backend (Remote Terminal Unit) is used in serial
	   communication and makes use of a compact, binary representation of
	   the data for	protocol communication.	The RTU	format follows the
	   commands/data with a	cyclic redundancy check	checksum as an error
	   check mechanism to ensure the reliability of	data. Modbus RTU is
	   the most common implementation available for	Modbus.	A Modbus RTU
	   message must	be transmitted continuously without inter-character
	   hesitations (extract	from Wikipedia,	Modbus,
	   http://en.wikipedia.org/wiki/Modbus (as of Mar. 13, 2011, 20:51
	   GMT).

	   The Modbus RTU framing calls	a slave, a device/service which	handle
	   Modbus requests, and	a master, a client which send requests.	The
	   communication is always initiated by	the master.

	   Many	Modbus devices can be connected	together on the	same physical
	   link	so before sending a message, you must set the slave (receiver)
	   with	modbus_set_slave(3). If	you're running a slave,	its slave
	   number will be used to filter received messages.

	   The libmodbus implementation	of RTU isn't time based	as stated in
	   original Modbus specification, instead all bytes are	sent as	fast
	   as possible and a response or an indication is considered complete
	   when	all expected characters	have been received. This
	   implementation offers very fast communication but you must take
	   care	to set a response timeout of slaves less than response timeout
	   of master (ortherwise other slaves may ignore master	requests when
	   one of the slave is not responding).

	   Create a Modbus RTU context

	       modbus_new_rtu(3)

	   Set the serial mode

	       modbus_rtu_get_serial_mode(3) modbus_rtu_set_serial_mode(3)
	       modbus_rtu_get_rts(3) modbus_rtu_set_rts(3)
	       modbus_rtu_set_custom_rts(3) modbus_rtu_get_rts_delay(3)
	       modbus_rtu_set_rts_delay(3)

       TCP (IPv4) Context
	   The TCP backend implements a	Modbus variant used for	communications
	   over	TCP/IPv4 networks. It does not require a checksum calculation
	   as lower layer takes	care of	the same.

	   Create a Modbus TCP context

	       modbus_new_tcp(3)

       TCP PI (IPv4 and	IPv6) Context
	   The TCP PI (Protocol	Independent) backend implements	a Modbus
	   variant used	for communications over	TCP IPv4 and IPv6 networks. It
	   does	not require a checksum calculation as lower layer takes	care
	   of the same.

	   Contrary to the TCP IPv4 only backend, the TCP PI backend offers
	   hostname resolution but it consumes about 1Kb of additional memory.

	   Create a Modbus TCP context

	       modbus_new_tcp_pi(3)

       Common
	   Before using	any libmodbus functions, the caller must allocate and
	   initialize a	modbus_t context with functions	explained above, then
	   the following functions are provided	to modify and free a context:

	   Free	libmodbus context

	       modbus_free(3)

	   Set slave ID

	       modbus_set_slave(3)

	   Enable debug	mode

	       modbus_set_debug(3)

	   Timeout settings

	       modbus_get_byte_timeout(3) modbus_set_byte_timeout(3)
	       modbus_get_response_timeout(3) modbus_set_response_timeout(3)

	   Error recovery mode

	       modbus_set_error_recovery(3)

	   Setter/getter of internal socket

	       modbus_set_socket(3) modbus_get_socket(3)

	   Information about header

	       modbus_get_header_length(3)

	   Macros for data manipulation

	       o   MODBUS_GET_HIGH_BYTE(data), extracts	the high byte from a
		   byte

	       o   MODBUS_GET_LOW_BYTE(data), extracts the low byte from a
		   byte

	       o   MODBUS_GET_INT64_FROM_INT16(tab_int16, index), builds an
		   int64 from the four first int16 starting at
		   tab_int16[index]

	       o   MODBUS_GET_INT32_FROM_INT16(tab_int16, index), builds an
		   int32 from the two first int16 starting at tab_int16[index]

	       o   MODBUS_GET_INT16_FROM_INT8(tab_int8,	index),	builds an
		   int16 from the two first int8 starting at tab_int8[index]

	       o   MODBUS_SET_INT16_TO_INT8(tab_int8, index, value), set an
		   int16 value into the	two first bytes	starting at
		   tab_int8[index]

	       o   MODBUS_SET_INT32_TO_INT16(tab_int16,	index, value), set an
		   int32 value into the	two first int16	starting at
		   tab_int16[index]

	       o   MODBUS_SET_INT64_TO_INT16(tab_int16,	index, value), set an
		   int64 value into the	four first int16 starting at
		   tab_int16[index]

	   Handling of bits and	bytes

	       modbus_set_bits_from_byte(3) modbus_set_bits_from_bytes(3)
	       modbus_get_byte_from_bits(3)

	   Set or get float numbers

	       modbus_get_float_abcd(3)	modbus_set_float_abcd(3)
	       modbus_get_float_badc(3)	modbus_set_float_badc(3)
	       modbus_get_float_cdab(3)	modbus_set_float_cdab(3)
	       modbus_get_float_dcba(3)	modbus_set_float_dcba(3)
	       modbus_get_float(3) (deprecated)	modbus_set_float(3)
	       (deprecated)

   Connection
       The following functions are provided to establish and close a
       connection with Modbus devices:

       Establish a connection

	   modbus_connect(3)

       Close a connection

	   modbus_close(3)

       Flush a connection

	   modbus_flush(3)

   Client
       The Modbus protocol defines different data types	and functions to read
       and write them from/to remote devices. The following functions are used
       by the clients to send Modbus requests:

       Read data

	   modbus_read_bits(3) modbus_read_input_bits(3)
	   modbus_read_registers(3) modbus_read_input_registers(3)
	   modbus_report_slave_id(3)

       Write data

	   modbus_write_bit(3) modbus_write_register(3)	modbus_write_bits(3)
	   modbus_write_registers(3)

       Write and read data

	   modbus_write_and_read_registers(3)

       Raw requests

	   modbus_send_raw_request(3) modbus_receive_confirmation(3)

       Reply an	exception

	   modbus_reply_exception(3)

   Server
       The server is waiting for request from clients and must answer when it
       is concerned by the request. The	libmodbus offers the following
       functions to handle requests:

       Data mapping: modbus_mapping_new(3) modbus_mapping_free(3)

       Receive

	   modbus_receive(3)

       Reply

	   modbus_reply(3) modbus_reply_exception(3)

ERROR HANDLING
       The libmodbus functions handle errors using the standard	conventions
       found on	POSIX systems. Generally, this means that upon failure a
       libmodbus function shall	return either a	NULL value (if returning a
       pointer)	or a negative value (if	returning an integer), and the actual
       error code shall	be stored in the errno variable.

       The modbus_strerror() function is provided to translate
       libmodbus-specific error	codes into error message strings; for details
       refer to	modbus_strerror(3).

MISCELLANEOUS
       The LIBMODBUS_VERSION_STRING constant indicates the libmodbus version
       the program has been compiled against. The variables
       libmodbus_version_major,	libmodbus_version_minor,
       libmodbus_version_micro give the	version	the program is linked against.

AUTHORS
       The libmodbus documentation was written by StA(C)phane Raimbault
       <stephane.raimbault@gmail.com>

RESOURCES
       Main web	site: http://www.libmodbus.org/

       Report bugs on the issue	tracker	at
       http://github.com/stephane/libmodbus/issues.

COPYING
       Free use	of this	software is granted under the terms of the GNU Lesser
       General Public License (LGPL v2.1+). For	details	see the	file
       COPYING.LESSER included with the	libmodbus distribution.

libmodbus v3.1.4		  04/29/2017			  LIBMODBUS(7)

NAME | SYNOPSIS | DESCRIPTION | ERROR HANDLING | MISCELLANEOUS | AUTHORS | RESOURCES | COPYING

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