Modbus in RDF

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

Introduction

Axiomatization

Classes

Data request

Data response

Data Field

Entity

Exception function

Exception response

Function

Function Field

A Modbus Message

Normal response

Payload

PayloadDataType

Request

Response

Exception code

Object Properties

hasEntity

hasFunction

hasPayloadDataType

Datatype Properties

hasAddress

hasCodeNumber

hasMostSignificantByte

hasMostSignificantWord

hasPollingTime

hasQuantity

hasTimeout

hasUnitID

hasZeroBasedAddressingFlag

Named Individuals

Coil

Discrete Input

Holding Register

Input Register

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

ILLEGAL FUNCTION

ILLEGAL DATA ADDRESS

ILLEGAL DATA VALUE

SLAVEDEVICE FAILURE

ACKNOWLEDGE

SLAVEDEVICE BUISY