QModbusRequest Class | Qt Serial Bus 5.6

Qt Documentation (Technology Preview) | Qt Serial Bus | C++ Classes | QModbusRequest

Qt 5.6.2 Reference Documentation

# 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 5.6
Inherits: | QModbusPdu

- List of all members, including inherited members

## Public Functions

| QModbusRequest() = default
| QModbusRequest(const QModbusPdu &pdu)
| QModbusRequest(FunctionCode code, const QByteArray &data = QByteArray())
| QModbusRequest(FunctionCode code, Args... data)

- 11 public functions inherited from QModbusPdu

## Static Public Members

int | calculateDataSize(const QModbusRequest &request)
int | minimumDataSize(const QModbusRequest &request)

- 1 static public member inherited from QModbusPdu

## Related Non-Members

QDataStream & | operator>>(QDataStream &stream, QModbusRequest &pdu)

### Additional Inherited Members

- 1 protected function inherited from QModbusPdu

## Detailed Description

QModbusRequest is a container class containing the function code and payload that is stored inside a Modbus ADU.

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 know 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 Function Documentation

### `[default]` QModbusRequest::QModbusRequest()

Constructs an invalid QModbusRequest.

### QModbusRequest::QModbusRequest(const QModbusPdu &pdu)

Constructs a copy of pdu.

### QModbusRequest::QModbusRequest(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(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.

### `[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.

### `[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.

## 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.