class QModbusRequest¶

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

Synopsis¶

Methods¶

def __init__()

Static functions¶

def calculateDataSize()
def minimumDataSize()

Note

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Detailed Description¶

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 known at compile time:

quint16 startAddress = 19, numberOfCoils = 10;
quint8 payloadInBytes = 2, outputHigh = 0xcd, outputLow = 0x01;
QModbusRequest request(QModbusRequest::WriteMultipleCoils, startAddress, numberOfCoils,
    payloadInBytes, outputHigh, outputLow);

__init__()¶

Constructs an invalid QModbusRequest .

__init__(pdu)

Parameters:: pdu – QModbusPdu

Constructs a copy of pdu.

__init__(code[, newData=QByteArray()])

Parameters:

code – FunctionCode
newData – 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.

static calculateDataSize(pdu)¶

Parameters:: pdu – QModbusRequest
Return type:: int

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.

See also

minimumDataSize registerDataSizeCalculator

static minimumDataSize(pdu)¶

Parameters:: pdu – QModbusRequest
Return type:: int

Returns the expected minimum data size for request based on the request’s function code; -1 if the function code is not known.