Thank you all.
I am using Windows unit, because of some other functions too.
I tried both solutions.
ASerge ReadKey function is still waiting for new line (enter key), same as standard Read.
RAW ReadKey function is working OK. In terminal mode it is waiting for key to be pressed (without new line enter key). There is working log present in GUI application.
Thaddy, GUI application just start terminal program and wait until it is finished (max few seconds), with disabled terminal / log window (readout only) GUI part. And during that time user doesn't need to press any keys, and I guess there is no issue with this. However, if there is working ASerge solution I can apply it.