That's good, thank you.
Apparently, it is not necessary to set the baud rate, they even could be different for both channels.
What makes the difference to a terminal emulator that needs the baud rate to be set?
Experimenting I found out:
When you run a terminal emulator (Hterm) prior to the B4J application then the baud rates you have set in Hterm to individual com ports is known to the B4J apllication. I used com3 (9600 baud) and com4 (38400), and other rates. I was wondering why B4J did not need to set the baud rate. So, that was the solution - but who knows why.