I´m new in Qt and doing Serial Communication. I need to make the connection between a GPS receiver and my PC, the connection is correct, and the reading is ok as well... but there is a problem, when a try to write and send commands to the GPS always got something wrong...
When I was able to send the information correctly, something strange happends. If a configure the GPS outside QT (RealTerm), and reconfigure with my code, the response that supose to give me just 2 short messages in the command window, get stuck with the same message and sends me infinite number of them

if there is no previous configuration, the program doesn't send anything, at least that seems to be.

This is my code

#include "myserial.h"
#include <QtSerialPort/QSerialPort>
#include <QObject>
#include <QtWidgets>
#include <QFile>
#include <QTextStream>

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

        //MySerialPort();

        MySerialPort iSerialPort;
        iSerialPort.openSerialPort();

        return a.exec();
}


MySerialPort::MySerialPort()
{

    serial = new QSerialPort(this);
    connect(serial, SIGNAL(readyRead()), this, SLOT(readData()));
    //openSerialPort();

}

void MySerialPort::openSerialPort()
{
    QString nombre;

    const auto infos = QSerialPortInfo::availablePorts();
    for (const QSerialPortInfo &info : infos) {
        QString puerto = info.portName();
        if ( info.manufacturer() == "Prolific" )
        {
            nombre = puerto;
            qDebug().noquote() << "El GPS se encuentra conectado en el puerto:" << nombre;
        }
    }

    serial->setPortName(nombre);
    serial->setBaudRate(QSerialPort::Baud9600);
    serial->setDataBits(QSerialPort::Data8);
    serial->setParity(QSerialPort::NoParity);
    serial->setStopBits(QSerialPort::OneStop);
    serial->setFlowControl(QSerialPort::NoFlowControl);
    if (serial->open(QIODevice::ReadWrite)) {

        showStatusMessage("Contectado a GPS");

    } else {

        showStatusMessage(tr("Open error"));
    }
}

void MySerialPort::closeSerialPort()
{
    if (serial->isOpen())
        serial->close();

    showStatusMessage(tr("Disconnected"));
}

void MySerialPort::sendData()
{
    static char Cf[]={0x40, 0x40, 0x43, 0x66, 0x25, 0x0D, 0x0A};
    for (int i=0; i < 7; i++)
        {
            serial->putChar(Cf[i]);
        }/*
    static char Gd[]={0x40, 0x40, 0x47, 0x64, 0x03, 0x20, 0x0D, 0x0A};
    for (int i=0; i < 8; i++)
        {
            serial->putChar(Gd[i]);
        }
    static char Ge[]={0x40, 0x40, 0x47, 0x65, 0x01, 0x23, 0x0D, 0x0A};
    for (int i=0; i < 8; i++)
        {
            serial->putChar(Ge[i]);
        }*/
    static char Hn[]={0x40, 0x40, 0x48, 0x6e, 0x02, 0x24, 0x0D, 0x0A};
    for (int i=0; i < 8; i++)
        {
            serial->putChar(Hn[i]);
        }

}

void MySerialPort::readData()
{

    sendData();


    QByteArray data = serial->readAll();

    // qDebug() << data;

    QByteArray received = data.toHex();

    qDebug()<<"testing :"<<received;


   


}

void MySerialPort::handleError(QSerialPort::SerialPortError error)
{
    if (error == QSerialPort::ResourceError) {
        closeSerialPort();
    }
}


void MySerialPort::showStatusMessage(const QString &message)
{
    qDebug() << message;
}

Any help would be nice, thank you