QModbusDevice Class

The QModbusDevice class is the base class for Modbus classes, QModbusServer and QModbusClient. More...

Header:	#include <QModbusDevice>
qmake:	QT += serialbus
Since:	Qt 5.8
Inherits:	QObject
Inherited By:	QModbusClient and QModbusServer

• List of all members, including inherited members

Public Types

enum	ConnectionParameter { SerialPortNameParameter, SerialParityParameter, SerialBaudRateParameter, SerialDataBitsParameter, SerialStopBitsParameter, …, NetworkAddressParameter }
enum	Error { NoError, ReadError, WriteError, ConnectionError, ConfigurationError, …, UnknownError }
enum	IntermediateError { ResponseCrcError, ResponseRequestMismatch }
enum	State { UnconnectedState, ConnectingState, ConnectedState, ClosingState }

Public Functions

	QModbusDevice(QObject *parent = nullptr)
virtual	~QModbusDevice()
bool	connectDevice()
QVariant	connectionParameter(QModbusDevice::ConnectionParameter parameter) const
QIODevice *	device() const
void	disconnectDevice()
QModbusDevice::Error	error() const
QString	errorString() const
void	setConnectionParameter(QModbusDevice::ConnectionParameter parameter, const QVariant &value)
QModbusDevice::State	state() const

Signals

void	errorOccurred(QModbusDevice::Error error)
void	stateChanged(QModbusDevice::State state)

Protected Functions

virtual void	close() = 0
virtual bool	open() = 0
void	setError(const QString &errorText, QModbusDevice::Error error)
void	setState(QModbusDevice::State newState)

Detailed Description

Member Type Documentation

enum QModbusDevice::ConnectionParameter

This enum describes the possible values that can be set for a Modbus device connection.

The general purpose value (and the associated types) are:

Constant	Value	Description
QModbusDevice::SerialPortNameParameter	0	This parameter holds the serial port used for device communication, e.g. COM1. QString
QModbusDevice::SerialParityParameter	1	This parameter holds the parity checking mode. QSerialPort::Parity
QModbusDevice::SerialBaudRateParameter	2	This parameter holds the data baud rate for the communication. QSerialPort::BaudRate
QModbusDevice::SerialDataBitsParameter	3	This parameter holds the data bits in a frame. QSerialPort::DataBits
QModbusDevice::SerialStopBitsParameter	4	This parameter holds the number of stop bits in a frame. QSerialPort::StopBits
QModbusDevice::NetworkPortParameter	5	This parameter holds the network port. int
QModbusDevice::NetworkAddressParameter	6	This parameter holds the host address for network communication. QString

enum QModbusDevice::Error

This enum describes all the possible error conditions.

Constant	Value	Description
QModbusDevice::NoError	0	No errors have occurred.
QModbusDevice::ReadError	1	An error occurred during a read operation.
QModbusDevice::WriteError	2	An error occurred during a write operation.
QModbusDevice::ConnectionError	3	An error occurred when attempting to open the backend.
QModbusDevice::ConfigurationError	4	An error occurred when attempting to set a configuration parameter.
QModbusDevice::TimeoutError	5	A timeout occurred during I/O. An I/O operation did not finish within a given time frame.
QModbusDevice::ProtocolError	6	A Modbus specific protocol error occurred.
QModbusDevice::ReplyAbortedError	7	The reply was aborted due to a disconnection of the device.
QModbusDevice::UnknownError	8	An unknown error occurred.

[since 6.0] enum QModbusDevice::IntermediateError

This enum describes possible errors that can happen during a full send and receive cycle for a Modbus reply.

Constant	Value	Description
QModbusDevice::ResponseCrcError	0	A Modbus response with a wrong CRC was received.
QModbusDevice::ResponseRequestMismatch	1	A Modbus response was received but did not match the open request, probably due to the PDU's function code not matching.

If any of the above intermediate errors occurred, the frame is likely resent until the maximum number of retries has been reached.

The list of intermediate errors can be inspected from the QModbusReply intermediate errors function.

This enum was introduced or modified in Qt 6.0.

See also QModbusClient::numberOfRetries() and QModbusReply::intermediateErrors().

enum QModbusDevice::State

This enum describes all possible device states.

Constant	Value	Description
QModbusDevice::UnconnectedState	0	The device is disconnected.
QModbusDevice::ConnectingState	1	The device is being connected.
QModbusDevice::ConnectedState	2	The device is connected to the Modbus network.
QModbusDevice::ClosingState	3	The device is being closed.

Member Function Documentation

QModbusDevice::QModbusDevice(QObject *parent = nullptr)

Constructs a Modbus device with the specified parent.

[signal] void QModbusDevice::errorOccurred(QModbusDevice::Error error)

This signal is emitted when an error of the type, error, occurs.

[signal] void QModbusDevice::stateChanged(QModbusDevice::State state)

This signal is emitted every time the state of the device changes. The new state is represented by state.

See also setState() and state().

[virtual] QModbusDevice::~QModbusDevice()

Destroys the QModbusDevice instance

[pure virtual protected] void QModbusDevice::close()

This function is responsible for closing the Modbus connection. The implementation must ensure that the instance's state() is set to QModbusDevice::UnconnectedState.

See also disconnectDevice().

bool QModbusDevice::connectDevice()

Connects the device to the Modbus network. Returns true if the connection process was successfully initiated; otherwise false. Final connection success confirmation requires the state() changing to QModbusDevice::ConnectedState.

This function calls open() as part of its implementation.

See also open().

QVariant QModbusDevice::connectionParameter(QModbusDevice::ConnectionParameter parameter) const

Returns the value associated with the given connection parameter. The returned value can be empty.

By default the QModbusDevice is initialized with some common values. The serial port settings are even parity, a baud rate of 19200 bits per second, eight data bits and one stop bit. The network settings for the host address is set to local host and port to 502.

See also setConnectionParameter() and ConnectionParameter.

[since 5.14] QIODevice *QModbusDevice::device() const

Returns the underlying QIODevice used for ModBus communication or nullptr if the device was not yet fully initialized.

This function was introduced in Qt 5.14.

void QModbusDevice::disconnectDevice()

Disconnects the device.

This function calls close() as part of its implementation.

QModbusDevice::Error QModbusDevice::error() const

Returns the error state of the device.

See also setError() and QModbusDevice::Error.

QString QModbusDevice::errorString() const

Returns descriptive error text for the device error.

See also QModbusDevice::Error.

[pure virtual protected] bool QModbusDevice::open()

This function is called by connectDevice(). Subclasses must provide an implementation that returns true on successful Modbus connection or connection initiation; otherwise returns false.

The implementation must ensure that the instance's state() is set to QModbusDevice::ConnectingState or QModbusDevice::ConnectedState upon success; otherwise QModbusDevice::UnconnectedState. Typically, QModbusDevice::ConnectingState is used when the connection process reports back asynchronously and QModbusDevice::ConnectedState in case of synchronous connect behavior.

See also connectDevice().

void QModbusDevice::setConnectionParameter(QModbusDevice::ConnectionParameter parameter, const QVariant &value)

Sets the value of parameter to value. If the parameter already exists, the previous value is overwritten. A active or running connection is not affected by such parameter changes.

See also ConnectionParameter and connectionParameter().

[protected] void QModbusDevice::setError(const QString &errorText, QModbusDevice::Error error)

Sets the error state of the device. ModBus device implementations must use this function in case of an error to set the error type and a descriptive errorText.

See also error() and QModbusDevice::Error.

[protected] void QModbusDevice::setState(QModbusDevice::State newState)

Sets the state of the device to newState. Modbus device implementations must use this function to update the device state.

See also state().

QModbusDevice::State QModbusDevice::state() const

Returns the current state of the device.

See also setState() and stateChanged().