why bytesAvailable() returns '0' when there are answer data from serial port monitor

[to_guliang]

As far as I remember bytesAvailable() doesn't work with QExtSerialPort.

supposed that bytesAvailable() doesn't work ,i amend my code as:

RS232->writeData(Data,13); //write data 
      usleep(120000);                  //wait 
 
      int i= RS232->QIODevice::bytesAvailable();//if there are bytes availble to read
 
      QString str;
      str.setNum(i);
      Com->setText(str);//show the bytes availble to read on the 'Com' Button
 
      char *pStr=NULL;
      RS232->read(pStr,13);    //read data from serial port to pStr
      Com1->setText(pStr);     //show the data on 'Com1' Button
      RS232->close();

RS232->writeData(Data,13); //write data 
      usleep(120000);                  //wait 
      
      int i= RS232->QIODevice::bytesAvailable();//if there are bytes availble to read
      
      QString str;
      str.setNum(i);
      Com->setText(str);//show the bytes availble to read on the 'Com' Button
    
      char *pStr=NULL;
      RS232->read(pStr,13);    //read data from serial port to pStr
      Com1->setText(pStr);     //show the data on 'Com1' Button
      RS232->close();

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i still can't get any data! why?

to zeratul: i don't use the serial monitor.