Thanks for your feedback. I have identified that the problem is due to the EDBG chip (usb-serial bridge) which requires DTR signal to enable the serial port RXD and TXD pins. Including the line of code "serial->setDataTerminalReady(true);" after opening the serial port, the serial port application is now working fine. I guess this is automatically carried out on hyper-terminal software and tera-term software. Whether the communication uses the flow control or not,some of the hardware bridge requires the flow control signals to be set for the first time after power ON.

Thanks !

Hi, Can you show your .pro file ?

Qt Designer is included in Qt sources and works only for UI files. Qt Creator (the IDE) is a separate application and a separate project. You need to install or compile it first, for example from qt.io/downloads. Once you have Qt Creator installer, you need to open the settings, add your Qt Version, then add a so called Kit (which is Qt Version + compiler bundle), and then you are ready to go. If you want to avoid all that hassle, use the Qt installer from the link above - it will install Qt, Qt Creator, and set everything up for you, completely automatically.

What version of Debian are you currently using ?

@LuAria please don't forget to mark your post as solved when your problem is finally gone :-)

@jsulm woooow! i add the spaces and the error disappear! REALLY REALLY thanks!!!!

@LeLev Thanks , I will try the same .