HTTP/2 200 server: GitHub.com content-type: text/html; charset=utf-8 last-modified: Thu, 09 Oct 2025 13:57:28 GMT access-control-allow-origin: * etag: W/"68e7bf48-8d18" expires: Thu, 09 Oct 2025 20:24:21 GMT cache-control: max-age=600 content-encoding: gzip x-proxy-cache: MISS x-github-request-id: CB33:379E10:F1126:11BAB1:68E8179B accept-ranges: bytes age: 0 date: Thu, 09 Oct 2025 20:14:21 GMT via: 1.1 varnish x-served-by: cache-bom-vanm7210022-BOM x-cache: MISS x-cache-hits: 0 x-timer: S1760040861.014126,VS0,VE291 vary: Accept-Encoding x-fastly-request-id: b039f9e7b7d9f1fa75de3fd3c72fbc04edcfa247 content-length: 4504

Vocabulary to represent Modbus messages in RDF.

This document is a work in progress

Introduction

To use in TD forms.

Axiomatization

Classes

Data request

IRI: https://www.w3.org/2019/wot/modbus#DataRequest

Data request contains additional information sent from a client to server that the server uses to take the action defined by the function code. This can include items like register address, the quantity of items to be handled, and the count of actual data bytes in the field. The data request field may be nonexistent (zero length) in certain kind of requests, in this case the server does not require any additional information. The function code alone specifies the action.

Sub-class of

Data Field

Data response

IRI: https://www.w3.org/2019/wot/modbus#DataResponse

Data response contains the information requested by the client to the server.

Sub-class of

Data Field

Data Field

IRI: https://www.w3.org/2019/wot/modbus#Data_Field

The Data Field of a Modbus messages can contain different kind of information: additional information that the server uses to take the action defined by the function code (data request), information regarding the performed action requested by the client (data response), information about the reason of the error (exception code).

Sub-class of	Payload
Super-class of	Data request Data response Exception code

Entity

IRI: https://www.w3.org/2019/wot/modbus#Entity

A Modbus registry type

Enumeration members

Coil Discrete Input Holding Register Input Register

Exception function

IRI: https://www.w3.org/2019/wot/modbus#ExceptionFunction

In case of error, the server replaces the normal function code with an exception function code (or error code) corresponding to the request function code +0x80.

Sub-class of

Function Field

Exception response

IRI: https://www.w3.org/2019/wot/modbus#ExceptionResponse

Response sent by server to client when error occurs.

Sub-class of

Response

Function

IRI: https://www.w3.org/2019/wot/modbus#Function

Function code identifies the operation requested by client, indicates to the server what kind of action to perform. For a normal response, the server simply echoes to the request the original function code.

Sub-class of	Function Field
Enumeration members	Read Single Coil Read Device Identification Read Discrete Inputs Read Multiple Holding Registers Read Multiple Input Registers Write Multiple Coils Write Multiple Holding Registers Write Single Coil Write Single Holding Register

Function Field

IRI: https://www.w3.org/2019/wot/modbus#Function_Field

Function Field class represents the value of the function in a Modbus frame. Each operation identified with a human readable name have a corresponding code. The response function code corresponds exactly to the request function code sent by the client when no error occurs. On the contrary, the response operation is identified with an error code or exception function code corresponding to the request function code + 0x80.

Sub-class of	Payload
Super-class of	Exception function Function

A Modbus Message

IRI: https://www.w3.org/2019/wot/modbus#Message

A Modbus Message class represents the communication between client and server

Super-class of

Request Response

Normal response

IRI: https://www.w3.org/2019/wot/modbus#NormalResponse

Response sent by server to client when no error occurs.

Sub-class of

Response

Payload

IRI: https://www.w3.org/2019/wot/modbus#Payload

In a Modbus message the content of a requested operation (sent by client to server) or of a response (elaborated by server and sent to client) is expressed with a specific code. This code is made by two field: function field and data field.

Super-class of

Data Field Function Field

PayloadDataType

IRI: https://www.w3.org/2019/wot/modbus#PayloadDataType

Represents the data types that can be used to define the payload content in Modbus messages.

Enumeration members

integer boolean string float decimal byte short int long unsignedByte unsignedShort unsignedInt unsignedLong double hexBinary

Request

IRI: https://www.w3.org/2019/wot/modbus#Request

A Request message is sent by a client device to a server device. The communication client/server stats only with a request sent by the client.

Sub-class of

A Modbus Message

Response

IRI: https://www.w3.org/2019/wot/modbus#Response

A Response message is sent by a server device to client device in return to a client's query.

Sub-class of	A Modbus Message
Super-class of	Exception response Normal response

Exception code

IRI: https://www.w3.org/2019/wot/modbus#ResponseCode

For an Exception Response, the server returns an exception code as data response field. Exception code defines the server condition that caused the exception as well as the reason of the error.

Sub-class of	Data Field
Enumeration members	ILLEGAL FUNCTION ILLEGAL DATA ADDRESS ILLEGAL DATA VALUE SLAVEDEVICE FAILURE ACKNOWLEDGE SLAVEDEVICE BUISY

Object Properties

hasEntity

IRI: https://www.w3.org/2019/wot/modbus#hasEntity

A registry type to let the runtime automatically detect the right function code

Domain	Request
Range	Entity

hasFunction

IRI: https://www.w3.org/2019/wot/modbus#hasFunction

Function Code sent by the master in every request. Specifying the desired interaction.

Domain	Normal response Request
Range	Function

hasPayloadDataType

IRI: https://www.w3.org/2019/wot/modbus#hasPayloadDataType

Specifies the data type contained in the request or response payload. Users can define the specific data type using a sub type of xsd:decimal.

Domain	Normal response Request
Range	PayloadDataType

Datatype Properties

hasAddress

IRI: https://www.w3.org/2019/wot/modbus#hasAddress

Specifies the starting address of the Modbus operations

Domain	Request
Range	integer

hasCodeNumber

IRI: https://www.w3.org/2019/wot/modbus#hasCodeNumber

Specifies the Modbus function/exception code number

Domain	Exception function Function Exception code
Range	integer

hasMostSignificantByte

IRI: https://www.w3.org/2019/wot/modbus#hasMostSignificantByte

When true, it describes that the byte order of the data in the Modbus message is the most significant byte first (i.e., Big-Endian). When false, it describes the least significant byte first (i.e., Little-Endian).

Domain	Request
Range	boolean

hasMostSignificantWord

IRI: https://www.w3.org/2019/wot/modbus#hasMostSignificantWord

When true, it describes that the word order of the data in the Modbus message is the most significant word first (i.e., no word swapping). When false, it describes the least significant word first (i.e. word swapping)

Domain	Request
Range	boolean

hasPollingTime

IRI: https://www.w3.org/2019/wot/modbus#hasPollingTime

Modbus TCP maximum polling rate. The Modbus specification does not define a maximum or minimum allowed polling rate, however specific implementations might introduce such limits. Defined as integer of milliseconds.

Domain	Request
Range	integer

hasQuantity

IRI: https://www.w3.org/2019/wot/modbus#hasQuantity

Specifies the amount of either registers or coils to be read or written to

Domain	Request
Range	integer

hasTimeout

IRI: https://www.w3.org/2019/wot/modbus#hasTimeout

Modbus response maximum waiting time. Defines how much time the runtime should wait until it receives a reply from the device.

Domain	Request
Range	integer

hasUnitID

IRI: https://www.w3.org/2019/wot/modbus#hasUnitID

The Unit ID is technically not needed for ModbusTCP, since the IP-address works as unique identifier, but for compatibility reasons it MUST be included

Domain	Request
Range	integer

hasZeroBasedAddressingFlag

IRI: https://www.w3.org/2019/wot/modbus#hasZeroBasedAddressingFlag

Modbus implementations can differ in the way addressing works, as the first coil/register can be either referred to as true or false.

Domain	Request
Range	boolean

Named Individuals

Coil

IRI: https://www.w3.org/2019/wot/modbus#Coil

Represent a modbus coil register. These entities can be read or written

Instance of

Entity

Discrete Input

IRI: https://www.w3.org/2019/wot/modbus#DiscreteInput

Represent a modbus discrete input. These entities can only be read

Instance of

Entity

Holding Register

IRI: https://www.w3.org/2019/wot/modbus#HoldingRegister

Represent a modbus holding register. These entities can be read or written

Instance of

Entity

Input Register

IRI: https://www.w3.org/2019/wot/modbus#InputRegister

Represent a modbus input register. These entities can only be read

Instance of

Entity

Read Single Coil

IRI: https://www.w3.org/2019/wot/modbus#readCoil

Read a single coil (i.e. boolean/bit access) value. Usually in the address range 00001-09999

Instance of

Function

Read Device Identification

IRI: https://www.w3.org/2019/wot/modbus#readDeviceIdentification

Read Device Identification for diagnostic purposes. Available in the majority of Modbus implementations.

Instance of

Function

Read Discrete Inputs

IRI: https://www.w3.org/2019/wot/modbus#readDiscreteInput

Read Physical Discrete Inputs (bit access). Address range 10001-19999

Instance of

Function

Read Multiple Holding Registers

IRI: https://www.w3.org/2019/wot/modbus#readHoldingRegisters

Read Multiple Holding Registers (16 bit access). Address range 40001-49999

Instance of

Function

Read Multiple Input Registers

IRI: https://www.w3.org/2019/wot/modbus#readInputRegisters

Read Multiple Physical Input Registers (16 bits). Address range 30001-39999

Instance of

Function

Write Multiple Coils

IRI: https://www.w3.org/2019/wot/modbus#writeMultipleCoils

Write Multiple Physical Coils (internal bits). Address range 00001-09999

Instance of

Function

Write Multiple Holding Registers

IRI: https://www.w3.org/2019/wot/modbus#writeMultipleHoldingRegisters

Write Multiple Holding Registers (output registers, 16 bit). Address range 40001-49999

Instance of

Function

Write Single Coil

IRI: https://www.w3.org/2019/wot/modbus#writeSingleCoil

Write Single Physical Coil (internal bit). Address range 00001-09999

Instance of

Function

Write Single Holding Register

IRI: https://www.w3.org/2019/wot/modbus#writeSingleHoldingRegister

Write Single HoldingRegister (internal bits). Address range 40001-49999

Instance of

Function

ILLEGAL FUNCTION

IRI: https://www.w3.org/2019/wot/modbus/errorCode#01

Function code received in the query is not recognized or allowed by slave

Instance of

Exception code

ILLEGAL DATA ADDRESS

IRI: https://www.w3.org/2019/wot/modbus/errorCode#02

Data address of some or all the required entities are not allowed or do not exist in slave

Instance of

Exception code

ILLEGAL DATA VALUE

IRI: https://www.w3.org/2019/wot/modbus/errorCode#03

Value is not accepted by slave

Instance of

Exception code

SLAVEDEVICE FAILURE

IRI: https://www.w3.org/2019/wot/modbus/errorCode#04

An unrecoverable error occurred while the slave was attempting to perform the requested action

Instance of

Exception code

ACKNOWLEDGE

IRI: https://www.w3.org/2019/wot/modbus/errorCode#05

The server has accepted the request and is processing it, but a long duration of time will be required to do so. This response is returned to prevent a timeout error from occurring in the client. The client can next issue a Poll Program Complete message to determine if processing is completed

Instance of

Exception code

SLAVEDEVICE BUISY

IRI: https://www.w3.org/2019/wot/modbus/errorCode#06

Slave is engaged in processing a long-duration command. Master should retry later

Instance of

Exception code