MODBUS_MANUAL

# MODBUS Manual

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# Function Code Categories

There are three categories of MODBUS Functions codes. They are :

#### Public Function Codes

- Are well defined function codes ,

- guaranteed to be unique,

- validated by the MODBUS.org community,

- publicly documented

- have available conformance test,

- includes both defined public assigned function codes as well as unassigned function codes reserved for future use.

#### User-Defined Function Codes

- there are two ranges of user-defined function codes, i.e. 65 to 72 and from 100 to 110 decimal.

- user can select and implement a function code that is not supported by the specification.

- there is no guarantee that the use of the selected function code will be unique

- if the user wants to re-position the functionality as a public function code, he must initiate an RFC to introduce the change into the public category and to have a new public function code assigned.

- MODBUS Organization, Inc expressly reserves the right to develop the proposed RFC.

#### Reserved Function Codes

- Function Codes currently used by some companies for legacy products and that are not available for public use.

- Informative Note: The reader is asked refer to Annex A (Informative) MODBUS RESERVED FUNCTION CODES, SUBCODES AND MEI TYPES.

# Public Function Code Definition