class QModbusPdu#

QModbusPdu is a abstract container class containing the function code and payload that is stored inside a Modbus ADU. More…

Inherited by: QModbusRequest

Synopsis#

Methods#

def __init__()
def data()
def dataSize()
def exceptionCode()
def functionCode()
def isException()
def isValid()
def setData()
def size()

Virtual methods#

def setFunctionCode()

Note

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Detailed Description#

The class provides access to the raw Modbus protocol packets as defined by the Modbus Application Protocol Specification 1.1b.

class ExceptionCode#

This enum describes all the possible error conditions as defined by Modbus Exception Codes. They are set by the server after checking the appropriate error conditions in the reply to a request and must be decoded by the client to operate on the exception code.

Constant

Description

QModbusPdu.IllegalFunction

Function code is not supported by device.

QModbusPdu.IllegalDataAddress

The received data address in the query is not an allowable address for the Modbus server.

QModbusPdu.IllegalDataValue

The contained value in the request data field is not an allowable value for the Modbus server.

QModbusPdu.ServerDeviceFailure

An irrecoverable error occurred while the server was attempting to perform the requested action.

QModbusPdu.Acknowledge

Specialized use in conjunction with programming commands.

QModbusPdu.ServerDeviceBusy

The server is engaged in processing a long duration program command.

QModbusPdu.NegativeAcknowledge

The server cannot perform the program function received in the query. This code is returned for an unsuccessful programming request. The client should request diagnostic or error information from the server.

QModbusPdu.MemoryParityError

Indicates that the extended file area failed to pass a consistency check. Used in conjunction with function codes 20 and 21. The exception code does not refer to any parity settings of the transmission line but only to the servers’ internal memory of file records.

QModbusPdu.GatewayPathUnavailable

Indicates that the gateway was unable to allocate an internal communication path from the input port to the output port for processing the request.

QModbusPdu.GatewayTargetDeviceFailedToRespond

Indicates that no response was obtained from the target device behind a gateway. Usually this means the target device is not online on the network.

QModbusPdu.ExtendedException

This is an extended exception as per Modbus specification. Generally this code is used to describe an exception that is otherwise further described.

Constant	Description
QModbusPdu.IllegalFunction	Function code is not supported by device.
QModbusPdu.IllegalDataAddress	The received data address in the query is not an allowable address for the Modbus server.
QModbusPdu.IllegalDataValue	The contained value in the request data field is not an allowable value for the Modbus server.
QModbusPdu.ServerDeviceFailure	An irrecoverable error occurred while the server was attempting to perform the requested action.
QModbusPdu.Acknowledge	Specialized use in conjunction with programming commands.
QModbusPdu.ServerDeviceBusy	The server is engaged in processing a long duration program command.
QModbusPdu.NegativeAcknowledge	The server cannot perform the program function received in the query. This code is returned for an unsuccessful programming request. The client should request diagnostic or error information from the server.
QModbusPdu.MemoryParityError	Indicates that the extended file area failed to pass a consistency check. Used in conjunction with function codes 20 and 21. The exception code does not refer to any parity settings of the transmission line but only to the servers’ internal memory of file records.
QModbusPdu.GatewayPathUnavailable	Indicates that the gateway was unable to allocate an internal communication path from the input port to the output port for processing the request.
QModbusPdu.GatewayTargetDeviceFailedToRespond	Indicates that no response was obtained from the target device behind a gateway. Usually this means the target device is not online on the network.
QModbusPdu.ExtendedException	This is an extended exception as per Modbus specification. Generally this code is used to describe an exception that is otherwise further described.

class FunctionCode#

Defines the function code and the implicit type of action required by the server. Not all Modbus devices can handle the same set of function codes.

Constant

Description

QModbusPdu.Invalid

Set by the default constructor, do not use.

QModbusPdu.ReadCoils

Requests the status of one or more coils from a device.

QModbusPdu.ReadDiscreteInputs

Requests the status of one or more input registers from a device.

QModbusPdu.ReadHoldingRegisters

Requests the status of one or more holding register values from a device.

QModbusPdu.ReadInputRegisters

Requests the status of one or more input register values from a device.

QModbusPdu.WriteSingleCoil

Requests to write a single coil on a device.

QModbusPdu.WriteSingleRegister

Requests to write a single holding register on a device.

QModbusPdu.ReadExceptionStatus

Requests the status of the eight Exception Status outputs on a device.

QModbusPdu.Diagnostics

Used to provide a series of tests for checking the client server communication system, or checking internal

QModbusPdu.GetCommEventCounter

Requests a status word and an event count from the device’s communication event counter.

QModbusPdu.GetCommEventLog

Requests a status word, event count, message count, and a field of event bytes from a device.

QModbusPdu.WriteMultipleCoils

Requests to write one or more coils on a device.

QModbusPdu.WriteMultipleRegisters

Requests to write one or more holding registers on a device.

QModbusPdu.ReportServerId

Requests the description of the type, the current status, and other information specific to a device.

QModbusPdu.ReadFileRecord

Requests a file record read.

QModbusPdu.WriteFileRecord

Requests a file record write.

QModbusPdu.MaskWriteRegister

Requests to modify the contents of a specified holding register using a combination of an AND or OR mask, and the register’s current contents.

QModbusPdu.ReadWriteMultipleRegisters

Requests the status of one or more holding register and at the same time to write one or more holding registers on a device.

QModbusPdu.ReadFifoQueue

Requests to read the contents of a First-In-First-Out (FIFO) queue of register in a remote device.

QModbusPdu.EncapsulatedInterfaceTransport

Please refer to Annex A of the Modbus specification.

QModbusPdu.UndefinedFunctionCode

Do not use.

Constant	Description
QModbusPdu.Invalid	Set by the default constructor, do not use.
QModbusPdu.ReadCoils	Requests the status of one or more coils from a device.
QModbusPdu.ReadDiscreteInputs	Requests the status of one or more input registers from a device.
QModbusPdu.ReadHoldingRegisters	Requests the status of one or more holding register values from a device.
QModbusPdu.ReadInputRegisters	Requests the status of one or more input register values from a device.
QModbusPdu.WriteSingleCoil	Requests to write a single coil on a device.
QModbusPdu.WriteSingleRegister	Requests to write a single holding register on a device.
QModbusPdu.ReadExceptionStatus	Requests the status of the eight Exception Status outputs on a device.
QModbusPdu.Diagnostics	Used to provide a series of tests for checking the client server communication system, or checking internal
QModbusPdu.GetCommEventCounter	Requests a status word and an event count from the device’s communication event counter.
QModbusPdu.GetCommEventLog	Requests a status word, event count, message count, and a field of event bytes from a device.
QModbusPdu.WriteMultipleCoils	Requests to write one or more coils on a device.
QModbusPdu.WriteMultipleRegisters	Requests to write one or more holding registers on a device.
QModbusPdu.ReportServerId	Requests the description of the type, the current status, and other information specific to a device.
QModbusPdu.ReadFileRecord	Requests a file record read.
QModbusPdu.WriteFileRecord	Requests a file record write.
QModbusPdu.MaskWriteRegister	Requests to modify the contents of a specified holding register using a combination of an AND or OR mask, and the register’s current contents.
QModbusPdu.ReadWriteMultipleRegisters	Requests the status of one or more holding register and at the same time to write one or more holding registers on a device.
QModbusPdu.ReadFifoQueue	Requests to read the contents of a First-In-First-Out (FIFO) queue of register in a remote device.
QModbusPdu.EncapsulatedInterfaceTransport	Please refer to Annex A of the Modbus specification.
QModbusPdu.UndefinedFunctionCode	Do not use.

__init__()#

Constructs an invalid QModbusPdu .

__init__(code, newData)

Parameters:

code – FunctionCode
newData – QByteArray

Constructs a QModbusPdu with function code set to code and payload set to data. The data is expected to be stored in big-endian byte order already.

__init__(arg__1)

Parameters:: arg__1 – QModbusPdu

Constructs a QModbusPdu that is a copy of other.

data()#

Return type:: QByteArray

Returns the PDU’s payload, excluding the function code. The payload is stored in big-endian byte order.

See also

setData()

dataSize()#

Return type:: int

Returns the PDU’s data size, excluding the function code.

exceptionCode()#

Return type:: ExceptionCode

Returns the response’s exception code.

functionCode()#

Return type:: FunctionCode

Returns the PDU’s function code.

See also

setFunctionCode()

isException()#

Return type:: bool

Returns true if the PDU contains an exception code; otherwise false.

isValid()#

Return type:: bool

Returns true if the PDU is valid; otherwise false.

A PDU is considered valid if the message code is in the range of 1 to 255 decimal and the PDU’s compound size (function code + data) does not exceed 253 bytes. A default constructed PDU is invalid.

setData(newData)#

Parameters:: newData – QByteArray

Sets the PDU’s function payload to data. The data is expected to be stored in big-endian byte order already.

See also

data()

setFunctionCode(code)#

Parameters:: code – FunctionCode

Sets the PDU’s function code to code.

See also

functionCode()

size()#

Return type:: int

Returns the PDU’s full size, including function code and data size.