class QModbusDevice

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

Inherited by: QModbusServer, QModbusTcpServer, QModbusRtuSerialServer, QModbusClient, QModbusTcpClient, QModbusRtuSerialClient

Synopsis

Methods

• def __init__()

• def connectDevice()

• def connectionParameter()

• def device()

• def disconnectDevice()

• def error()

• def errorString()

• def setConnectionParameter()

• def setError()

• def setState()

• def state()

Virtual methods

• def close()

• def open()

Signals

• def errorOccurred()

• def stateChanged()

Note

This documentation may contain snippets that were automatically translated from C++ to Python. We always welcome contributions to the snippet translation. If you see an issue with the translation, you can also let us know by creating a ticket on https:/bugreports.qt.io/projects/PYSIDE

Detailed Description

class Error

This enum describes all the possible error conditions.

Constant	Description
QModbusDevice.NoError	No errors have occurred.
QModbusDevice.ReadError	An error occurred during a read operation.
QModbusDevice.WriteError	An error occurred during a write operation.
QModbusDevice.ConnectionError	An error occurred when attempting to open the backend.
QModbusDevice.ConfigurationError	An error occurred when attempting to set a configuration parameter.
QModbusDevice.TimeoutError	A timeout occurred during I/O. An I/O operation did not finish within a given time frame.
QModbusDevice.ProtocolError	A Modbus specific protocol error occurred.
QModbusDevice.ReplyAbortedError	The reply was aborted due to a disconnection of the device.
QModbusDevice.UnknownError	An unknown error occurred.
QModbusDevice.InvalidResponseError	An error occurred while parsing the response, or the FunctionCode is not supported by the current implementation. In the latter case custom Modbus client implementation can override the processResponse() and processPrivateResponse() methods to provide support for needed functions.

class State

This enum describes all possible device states.

Constant	Description
QModbusDevice.UnconnectedState	The device is disconnected.
QModbusDevice.ConnectingState	The device is being connected.
QModbusDevice.ConnectedState	The device is connected to the Modbus network.
QModbusDevice.ClosingState	The device is being closed.

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

class IntermediateError

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

Constant	Description
QModbusDevice.ResponseCrcError	A Modbus response with a wrong CRC was received.
QModbusDevice.ResponseRequestMismatch	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.

See also

numberOfRetries() intermediateErrors()

__init__([parent=None])

Parameters:

parent – QObject

Constructs a Modbus device with the specified parent.

abstract close()

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

See also

disconnectDevice()

connectDevice()

Return type:

bool

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 ConnectedState .

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

See also

open()

connectionParameter(parameter)

Parameters:

parameter – ConnectionParameter

Return type:

object

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.

Note

For a serial connection to succeed, the SerialPortNameParameter needs to be set to a valid communication port. The information about valid serial ports can be obtained from QSerialPortInfo.

Note

If the device is already connected, the settings are taken into account after reconnecting the device.

See also

setConnectionParameter() ConnectionParameter

device()

Return type:

QIODevice

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

Note

Do not store a pointer to the underlying device, because it can be invalidated at any point in time.

disconnectDevice()

Disconnects the device.

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

error()

Return type:

Error

Returns the error state of the device.

See also

setError() Error

errorOccurred(error)

Parameters:

error – Error

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

errorString()

Return type:

str

Returns descriptive error text for the device error.

See also

Error

abstract open()

Return type:

bool

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 ConnectingState or ConnectedState upon success; otherwise UnconnectedState . Typically, ConnectingState is used when the connection process reports back asynchronously and ConnectedState in case of synchronous connect behavior.

See also

connectDevice()

setConnectionParameter(parameter, value)

Parameters:

• parameter – ConnectionParameter

• value – object

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 connectionParameter()

setError(errorText, error)

Parameters:

• errorText – str

• 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() Error

setState(newState)

Parameters:

newState – State

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

See also

state()

state()

Return type:

State

Returns the current state of the device.

See also

setState() stateChanged()

stateChanged(state)

Parameters:

state – State

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

See also

setState() state()