Modbus Functions

General Description

The Modbus protocol offers functions for reading or writing data on the Modbus network. This protocol also offers diagnostic and network management functions.

Only Modbus functions managed by the I/O Smart Link device are described here.

Table of Modbus Functions

The following table describes in detail the functions supported by I/O Smart Link devices:

Function code	Sub-Function code	Function Name
01	–	Read n output or internal bits
02	–	Read n input bits
03	–	Read n output or internal words
05	–	Write 1 bit
06	–	Write 1 word
08	⁽¹⁾	Modbus diagnostics
15	–	Write n bits
16	–	Write n words
43	14⁽²⁾	Read identification
	15⁽³⁾	Read the date and time
	16⁽⁴⁾	Write the date and time
100	4⁽⁵⁾	Read n non-adjacent words where n ≤ 100. NOTE: Thanks to the read distributed holding register function, the user can: Avoid reading a large block of adjacent words when only a few words are needed. Avoid multiple use of function 3 in order to read non-adjacent words.
(1) For more details, see the appendix describing function 8 (2) For more details, see the appendix describing function 43–14 (3) For more details, see the appendix describing function 43-15 (4) For more details, see the appendix describing function 43-16 (5) For more details, see the appendix describing function 100-4

NOTE: For more information, a detailed description of the Modbus protocol is available on www.modbus.org.