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Generate a modbus read class

In order to make the plugin development for modbus TCP devices much easier and faster, a small tool has been developed to generate a modbus TCP master based class providing get and set methods for the registers and property changed signals.

The workflow looks like this:

Write the registers.json file containing all register information you are interested to.
Run the script and provide the class name, output directory and the path to the JSON file
Include the generated class in your plugin, connect the <propertyName>Changed() signal and update the thing state within the plugin.

The class will provide 2 main methods for fetching information from the modbus device:

initialize() will read all registers with "readSchedule": "init" and emits the signal initializationFinished() once all replies returned.
update() can be used to update all registers with "readSchedule": "update". The class will then fetch each register and update the specified value internally. If the value has changed, the <propertyName>Changed() signal will be emitted.

The reulting class will inhert from the ModbusTCPMaster class, providing easy access to all possible modbus operations and inform about the connected state.

JSON format

The basic structure of the modbus register JSON looks like following example:

{
    "enums": [
        {
            "name": "NameOfEnum",
            "values": [
                {
                    "key": "EnumValue1",
                    "value": 0
                },
                {
                    "key": "EnumValue2",
                    "value": 1
                },
                ....
            ]
        }
    ],
    "registers": [
        {
            "id": "registerPropertyName",
            "address": 4,
            "size": 1,
            "type": "uint16",
            "readSchedule": "init",
            "description": "Description of the register",
            "unit": "V",
            "defaultValue": "0",
            "access": "RO"
        },
        {
            "id": "registerWithEnumValues",
            "address": 5,
            "size": 1,
            "type": "uint16",
            "readSchedule": "update",
            "enum": "NameOfEnum",
            "defaultValue": "NameOfEnumEnumValue1",
            "description": "Description of the enum register like states",
            "access": "RO"
        },
        ...
    ]
}

Enums

Many modbus devices provide inforation using Enums, indicating a special state trough a defined list of values. If a register implements an enum, you can define it in the enums section. The name property defines the name of the enum, and the script will generate a c++ enum definition from this section. Each enum value will then be generated using <EnumName><EnumValueName> = <value>.

If a register represets an enum, you simply add the property "enum": "NameOfEnum" in the register map and the property will be defined using the resulting enum type. All convertion between enum and resulting modbus register value will be done automatically.

Registers

Earch register will be defined as a property in the resulting class modbus TCP class providing easy access to the register data.

id: Mandatory. The id defines the name of the property used in the resulting class.
address: Mandatory. The modbus address of the register.
size: Mandatory. The amount of registers to read for the property.
type: Mandatory. The data type of this property. Available data types are:
- uint16 : will be converted to quint16
- int16 : will be converted to qint16
- uint32 : will be converted to quint32
- int32 : will be converted to qint32
- uint64 : will be converted to quint64
- int64 : will be converted to qint64
- float: will be converted to float
- float64: will be converted to double
- string : will be converted to QString
readSchedule: Optional. Defines when the register needs to be fetched. If no read schedule has been defined, the class will provide only the update methods, but will not read the value during initialize() or update() calls. Possible values are:
- init: The register will be fetched during initialization. Once all init registers have been fetched, the initializationFinished() signal will be emitted.
- update: The register will be feched each time the update() method will be called.
enum: Optional: If the given data type represents an enum value, this propery can be set to the name of the used enum from the enum definition. The class will take care internally about the data convertion from and to the enum values.
description: Mandatory. A clear description of the register.
unit: Optional. Represents the unit of this register value.
registerType: Optional. Represents the type of the register and how to read/write it. Default is holdingRegister. Possible values are:
- holdingRegister
- inputRegister
- coils
- discreteInputs
access: Mandatory. Describes the access to this register. Possible valies are:
- RO: Read only access. Only the get method and the changed singal will be defined.
- RW: Read and write access. Also a set mehtod will be defined.
- WO: Write only. Only the set method will be defined.
scaleFactor: Optional. The name of the scale factor register to convert this value to float. floatValue = intValue * 10^scaleFactor value. The scale factor value is normally a int16 value, i.e. -10 or 10
staticScaleFactor: Optional. Use this static scale factor to convert this register value to float. floatValue = registerValue * 10^staticScaleFactor. The scale factor value is normally a int16 value, i.e. -10 or 10
defaultValue: Optional. The value for initializing the property.

Example

Change into your plugin sub directory. Assuming you wrote the registers.json file you can run now following command to generate your modbus class:

$ python3 ../modbus/tools/generate-connection.py -j registers.json -o . -c MyModbusConnection

You the result will be a header and a source file called:

mymodbusconnection.h
mymodbusconnection.cpp

You can include this class in your project and provide one connection per thing.

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