问QModbusTcpClient无法连接到可编程控制器

EN

    PLC = new QModbusTcpClient();
    m_port = 502;
    m_host = "10.100.101.2"; //PLC IP
    PLC->setConnectionParameter(QModbusDevice::NetworkPortParameter, this->m_port);
    PLC->setConnectionParameter(QModbusDevice::NetworkAddressParameter, this->m_host);
    PLC->setTimeout(5000);
    PLC->setNumberOfRetries(10);

    qDebug()<<"State: " << PLC->state();

    qDebug()<<"Try to connect...";
    if(!PLC->connectDevice()){
        qDebug()<<"Not connected to PLC: " << PLC->errorString();

    }
    else{
        qDebug()<<"State: " << PLC->state();

        while(PLC->state()!=QModbusDevice::ConnectedState){
        QThread::msleep(5);
        }
        qDebug()<<"Connection to PLC succesed" << PLC->state();
        emit PLCConnected();
    }