QModbusRequest Class
QModbusRequest is a container class containing the function code and payload that is stored inside a Modbus ADU. More...
| Header: | #include <QModbusRequest> |
| qmake: | QT += serialbus |
| Since: | Qt 5.8 |
| Inherits: | QModbusPdu |
This class was introduced in Qt 5.8.
Public Types
| (alias) | CalcFuncPtr |
Public Functions
| QModbusRequest(QModbusPdu::FunctionCode code, Args... data) | |
| QModbusRequest(QModbusPdu::FunctionCode code, const QByteArray &data = QByteArray()) | |
| QModbusRequest(const QModbusPdu &pdu) | |
| QModbusRequest() |
Static Public Members
| int | calculateDataSize(const QModbusRequest &request) |
| int | minimumDataSize(const QModbusRequest &request) |
| void | registerDataSizeCalculator(QModbusPdu::FunctionCode fc, QModbusRequest::CalcFuncPtr calculator) |
Related Non-Members
| QDataStream & | operator>>(QDataStream &stream, QModbusRequest &pdu) |
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"));
Note: 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
This is a type alias for decltype(&calculateDataSize).
Typedef for a pointer to a custom calculator function with the same signature as QModbusRequest::calculateDataSize.
Member Function Documentation
template <typename Args> 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.
Note: 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.
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(const QModbusPdu &pdu)
Constructs a copy of pdu.
QModbusRequest::QModbusRequest()
Constructs an invalid QModbusRequest.
[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 minimumDataSize and 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.
Note: 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.