When QT serial port reads data, it will wait a very long time, which is basically fixed between 150-250ms. With the same serial port assistant, it takes about 40-50ms to read the parameters.

//
serial->readAll();
serial->write(sendData);
 while(serial->bytesAvailable()<39) 
{ if (!serial->waitForReadyRead(10)) 
{ serial->readyRead();
 QCoreApplication::processEvents(QEventLoop::AllEvents, 50); } }
 revData += serial->readAll();