QModbusRequest Class▲
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Header: QModbusRequest
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Since: Qt 5.8
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CMake:
find_package(Qt6 REQUIRED COMPONENTS SerialBus)
target_link_libraries(mytarget PRIVATE Qt6::SerialBus)
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qmake: QT += serialbus
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Inherits: QModbusPdu
Detailed Description▲
A Modbus request usually consists of a single byte describing the FunctionCode and N bytes of payload
A typical Modbus request can looks like this:
QModbusRequest request(QModbusRequest::WriteMultipleCoils,
QByteArray::fromHex("0013000a02cd01"));When using the constructor taking the QByteArray, please make sure to convert the containing data to big-endian byte order before creating the request.
The same request can be created like this, if the values are known at compile time:
quint16 startAddress = 19, numberOfCoils = 10;
quint8 payloadInBytes = 2, outputHigh = 0xcd, outputLow = 0x01;
QModbusRequest request(QModbusRequest::WriteMultipleCoils, startAddress, numberOfCoils,
payloadInBytes, outputHigh, outputLow);Member Type Documentation▲
[alias] QModbusRequest::CalcFuncPtr▲
Typedef for a pointer to a custom calculator function with the same signature as QModbusRequest::calculateDataSize.
Member Function Documentation▲
QModbusRequest::QModbusRequest()▲
Constructs an invalid QModbusRequest.
QModbusRequest::QModbusRequest(const QModbusPdu &pdu)▲
Constructs a copy of pdu.
[explicit] QModbusRequest::QModbusRequest(QModbusPdu::FunctionCode code, const QByteArray &data = QByteArray())▲
Constructs a QModbusResponse with function code set to code and payload set to data. The data is expected to be stored in big-endian byte order already.
QModbusRequest::QModbusRequest(QModbusPdu::FunctionCode code, Args... data)▲
Constructs a QModbusRequest with function code set to code and payload set to data. The data is converted and stored in big-endian byte order.
Usage is limited quint8 and quint16 only. This is because QDataStream stream operators will not only append raw data, but also e.g. size, count, etc. for complex types.
[static] int QModbusRequest::calculateDataSize(const QModbusRequest &request)▲
Calculates the expected data size for request based on the request's function code and data. Returns the full size of the request's data part; -1 if the size could not be properly calculated.
See Also▲
See also minimumDataSize, registerDataSizeCalculator
[static] int QModbusRequest::minimumDataSize(const QModbusRequest &request)▲
Returns the expected minimum data size for request based on the request's function code; -1 if the function code is not known.
[static] void QModbusRequest::registerDataSizeCalculator(QModbusPdu::FunctionCode fc, QModbusRequest::CalcFuncPtr calculator)▲
This function registers a user-defined implementation to calculate the request data size for function code fc. It can be used to extend or override the implementation inside QModbusRequest::calculateDataSize().
The CalcFuncPtr is a typedef for a pointer to a custom calculator function with the following signature:
int myCalculateDataSize(const QModbusRequest &pdu);Related Non-Members▲
QDataStream &operator>>(QDataStream &stream, QModbusRequest &pdu)▲
Reads a pdu from the stream and returns a reference to the stream.
The function might fail to properly stream PDU's with function code QModbusPdu::Diagnostics or QModbusPdu::EncapsulatedInterfaceTransport because of the missing size indicator inside the PDU. In particular this may happen when the PDU is embedded into a stream that doesn't end with the diagnostic/encapsulated request itself.