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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 |
QModbusRequest(QModbusPdu::FunctionCode code, Args... data) | |
QModbusRequest(QModbusPdu::FunctionCode code, const QByteArray &data = QByteArray()) | |
QModbusRequest(const QModbusPdu &pdu) | |
QModbusRequest() |
int | calculateDataSize(const QModbusRequest &request) |
int | minimumDataSize(const QModbusRequest &request) |
void | registerDataSizeCalculator(QModbusPdu::FunctionCode fc, QModbusRequest::CalcFuncPtr calculator) |
QDataStream & | operator>>(QDataStream &stream, QModbusRequest &pdu) |
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);
[alias]
QModbusRequest::CalcFuncPtrTypedef for a pointer to a custom calculator function with the same signature as QModbusRequest::calculateDataSize.
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.
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.
Constructs a copy of pdu.
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);
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.