QModbusServer Class

Member Function Documentation

QModbusServer::QModbusServer(QObject *parent = nullptr)

Constructs a Modbus server with the specified parent.

bool QModbusServer::data(QModbusDataUnit *newData) const

Returns the values in the register range given by newData.

newData must provide a valid register type, start address and valueCount. The returned newData will contain the register values associated with the given range.

If newData contains a valid register type but a negative start address the entire register map is returned and newData appropriately sized.

See also setData().

bool QModbusServer::data(QModbusDataUnit::RegisterType table, quint16 address, quint16 *data) const

Reads data stored in the Modbus server. A Modbus server has four tables (table) and each have a unique address field, which is used to read data from the desired field. See QModbusDataUnit::RegisterType for more information about the different tables. Returns false if address is outside of the map range or the register type is not even defined.

See also QModbusDataUnit::RegisterType and setData().

[signal] void QModbusServer::dataWritten(QModbusDataUnit::RegisterType table, int address, int size)

This signal is emitted when a Modbus client has written one or more fields of data to the Modbus server. The signal contains information about the fields that were written:

• Register type (table) that was written,
• address of the first field that was written,
• and size of consecutive fields that were written starting from address.

The signal is not emitted when the to-be-written fields have not changed due to no change in value.

[virtual protected] QModbusResponse QModbusServer::processPrivateRequest(const QModbusPdu &request)

This function should be implemented by custom Modbus servers. It is called by processRequest() if the given request is not a standard Modbus request.

Overwriting this function allows handling of additional function codes and subfunction-codes not specified in the Modbus Application Protocol Specification 1.1b. Reimplementations should call this function again to ensure an exception response is returned for all unknown function codes the custom Modbus implementation does not handle.

This default implementation returns a QModbusExceptionResponse with the request function code and error code set to illegal function.

See also processRequest().

[virtual protected] QModbusResponse QModbusServer::processRequest(const QModbusPdu &request)

Processes a Modbus client request and returns a Modbus response. This function returns a QModbusResponse or QModbusExceptionResponse depending on the nature of the request.

The default implementation of this function handles all standard Modbus function codes as defined by the Modbus Application Protocol Specification 1.1b. All other Modbus function codes not included in the specification are forwarded to processPrivateRequest().

The default handling of the standard Modbus function code requests can be overwritten by reimplementing this function. The override must handle the request type in question and return the appropriate QModbusResponse. A common reason might be to filter out function code requests for data values to limit read/write access and function codes not desired in particular implementations such as serial line diagnostics on ethernet or Modbus Plus transport layers. Every other request type should be forwarded to this default implementation.

Note: This function should not be overridden to provide a custom implementation for non-standard Modbus request types.

See also processPrivateRequest().

[virtual] bool QModbusServer::processesBroadcast() const

Subclasses should implement this function if the transport layer shall handle broadcasts. The implementation then should return true if the currently processed request is a broadcast request; otherwise false. The default implementation returns always false.

Note: The return value of this function only makes sense from within processRequest() or processPrivateRequest(), otherwise it can only tell that the last request processed was a broadcast request.

[virtual protected] bool QModbusServer::readData(QModbusDataUnit *newData) const

Reads the values in the register range given by newData and writes the data back to newData. Returns true on success or false if newData is 0, the newData range is outside of the map range or the registerType() does not exist.

Note: Sub-classes that implement reading from a different backing store then default one, also need to implement setMap() and writeData().

See also setMap() and writeData().

int QModbusServer::serverAddress() const

Returns the address of this Mobus server instance.

See also setServerAddress().

bool QModbusServer::setData(const QModbusDataUnit &newData)

Writes newData to the Modbus server map. Returns false if the newData range is outside of the map range.

If the call was successful the dataWritten() signal is emitted. Note that the signal is not emitted when the addressed register has not changed. This may happen when newData contains exactly the same values as the register already. Nevertheless this function returns true in such cases.

See also data().

bool QModbusServer::setData(QModbusDataUnit::RegisterType table, quint16 address, quint16 data)

Writes data to the Modbus server. A Modbus server has four tables (table) and each have a unique address field, which is used to write data to the desired field. Returns false if address outside of the map range.

If the call was successful the dataWritten() signal is emitted. Note that the signal is not emitted when data has not changed. Nevertheless this function returns true in such cases.

See also QModbusDataUnit::RegisterType, data(), and dataWritten().

[virtual] bool QModbusServer::setMap(const QModbusDataUnitMap &map)

Sets the registered map structure for requests from other ModBus clients to map. The register values are initialized with zero. Returns true on success; otherwise false.

If this function is not called before connecting, a default register with zero entries is setup.

Note: Calling this function discards any register value that was previously set.

void QModbusServer::setServerAddress(int serverAddress)

Sets the address for this Modbus server instance to serverAddress.

See also serverAddress().

[virtual] bool QModbusServer::setValue(int option, const QVariant &newValue)

Sets the newValue for option and returns true on success; false otherwise.

Note: If the option's associated type is quint8 or quint16 and the type of newValue is larger, the data will be truncated or conversation will fail.

See also value().

[virtual] QVariant QModbusServer::value(int option) const

Returns the value for option or an invalid QVariant if the option is not set.

See also setValue().

[virtual protected] bool QModbusServer::writeData(const QModbusDataUnit &newData)

Writes newData to the Modbus server map. Returns true on success, or false if the newData range is outside of the map range or the registerType() does not exist.

Note: Sub-classes that implement writing to a different backing store then default one, also need to implement setMap() and readData(). The dataWritten() signal needs to be emitted from within the functions implementation as well.

See also setMap(), readData(), and dataWritten().