recieve continious data from serial port

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I have a problem while reading data from microcontroller...my microcontroller sends char 'a' continiously(just to test)..and I want to receive the character in my ui application..(lineedit)...

QextSerialPort * port = new QextSerialPort("COM4", QextSerialPort::EventDriven);
    port->setBaudRate(BAUD9600);
    port->setFlowControl(FLOW_OFF);
    port->setParity(PAR_NONE);
    port->setDataBits(DATA_8);
    port->setStopBits(STOP_1);
    port->open(QIODevice::ReadWrite);
    port->setTimeout(500);
    port->setRts(true);
    port->setDtr(true);
    if(port->isReadable())
    {
    char buff[1024];
    qint64 i=port->readLine(buff,1024);
 
    buff[i]='\0';
    QString str(buff);
    if(i!=-1)
    {
    ui->lineEdit->setText(str);;
    port->close();
}
}
 
else
    qDebug("port not open");

QextSerialPort * port = new QextSerialPort("COM4", QextSerialPort::EventDriven);
    port->setBaudRate(BAUD9600);
    port->setFlowControl(FLOW_OFF);
    port->setParity(PAR_NONE);
    port->setDataBits(DATA_8);
    port->setStopBits(STOP_1);
    port->open(QIODevice::ReadWrite);
    port->setTimeout(500);
    port->setRts(true);
    port->setDtr(true);
    if(port->isReadable())
    {
    char buff[1024];
    qint64 i=port->readLine(buff,1024);
    
    buff[i]='\0';
    QString str(buff);
    if(i!=-1)
    {
    ui->lineEdit->setText(str);;
    port->close();
}
}

else
    qDebug("port not open");

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this does not help me ............please help me/...