i am trying to write to perform a read/write operation on the above device which require command. the control come from the host to the device and if the device would respond appropriately. the device is a motorized IC/magnetic card reader/writer.
Qt Code: 
  1. #include "mainwindow.h"
  2. #include "ui_mainwindow.h"
  3. #include <QtCore>
  4. #include <QtGui>
  5. #include "databaseconnection.h";
  6. #include <mythread.h>
  7. #include <QThread>
  8. #include <QMutex>
  9. #include "mysecondthread.h"
  10. #include <QtSql>
  11. #include <QDebug>
  12. #include "qextserialport.h"
  13. #include "qextserialenumerator.h"
  14. QextSerialPort *port = new QextSerialPort("COM1",QextSerialPort::EventDriven);
  15. MainWindow::MainWindow(QWidget *parent) :
  16.     QMainWindow(parent),
  17.     ui(new Ui::MainWindow)
  18. {
  19.    // if(databaseconnection::databse()){
  20.    //     QMessageBox::information(this,"connected","connected");
  21.    // }
  22.    // else if(!(databaseconnection::databse())){
  23.    //    QMessageBox::information(this,"connected failed","failed");
  24.    // }
  25.     Mythread cob;
  26.      port=new QextSerialPort();
  27.      port->setBaudRate(BAUD9600);
  28.          port->setFlowControl(FLOW_XONXOFF);
  29.          port->setParity(PAR_NONE);
  30.          port->setDataBits(DATA_8);
  31.          port->setStopBits(STOP_1);
  32.          port->open(QIODevice::ReadWrite);
  33.          connect(port,SIGNAL(readyRead()),this,SLOT(on_pushButton_clicked()));
  34.  QList<QextPortInfo> ports = QextSerialEnumerator::getPorts();
  35.  
  36.     ui->setupUi(this);
  37.     foreach (QextPortInfo info, ports) {
  38.         qDebug() << "port name:"       << info.portName;
  39.         ui->portlab->addItem(info.portName);
  40.     }
  41. }
  42.  
  43. MainWindow::~MainWindow()
  44. {
  45.     delete ui;
  46. }
  47.  
  48. void MainWindow::on_pushButton_clicked()
  49. {
  50.  
  51.  
  52. //qDebug()<<"no data to read";
  53.        if(port->isOpen()){
  54.            QByteArray command="0x03";
  55.  
  56.                QString data = port->readAll();
  57. if(port->write(command.toHex())){
  58.     qDebug()<<"written";
  59. }
  60.  
  61. if(data==""){
  62.                    qDebug()<<"no data to read"<<data;
  63.                   ui->labelread->setText("wait while trying to read="+data);
  64.                }
  65.                else if(data.size()==3&& (data.startsWith("H"))){
  66.  qDebug()<<data;
  67.  ui->labelread->setText("the data read="+data);
  68.  
  69.               } //data.data();
  70.  
  71.  
  72.  
  73.  
  74.           // QMessageBox::information(this,"opened","opened");
  75.        }
  76.        else{
  77.            QMessageBox::warning(this,"error","error");
  78.        }
  79.             //connect(port, SIGNAL(readyRead()), this, SLOT(onDataAvailable()));
  80. //port->open();
  81.  
  82. }
  83.  
  84. void MainWindow::on_pushButton_2_clicked()
  85. {
  86.     QString bb,idn;
  87.              bb= "oloo";
  88.              idn="9000";
  89.              QSqlQuery query;
  90.                   query.prepare("INSERT INTO user (name, idno) "
  91.                                 "VALUES (:name, :idno)");
  92.                   query.bindValue(":name", bb);
  93.                   query.bindValue(":idno", idn);
  94.  
  95.                  // query.exec();
  96.                   if(query.exec()){
  97.                       qDebug()<<" inserted connected";
  98.  
  99.  
  100.                   }else{
  101.                       qDebug()<<" not insert connected";
  102.                   }
  103. }
  104.  
  105. void MainWindow::on_pushButton_3_clicked()
  106. {
  107.     if(port->isOpen()){
  108.         QString n="0x02";
  109.         QByteArray command;
  110.  
  111.             QString data = port->readAll();
  112. if(port->write(command.append(n))){
  113.  qDebug()<<"written";
  114. }
  115. else{
  116.    qDebug()<<" not written";
  117. }
  118.     }
  119. }
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am not able to receive any response from the device.