Thank you for information and for your hints!
In this case i want to check the status byte from RN2483 every hour. Bit number 4 shows the Join status (‘0’ – network not joined, ‘1’ – network joined).
But here i got another strange problem - if i implement this in my code, suddenly on microcontroller side the RX-Interrupt will not be triggered anymore.
And this has to do (so i am sure) with the RN2483 sleep mode, because it works when the module is not in sleep mode.
But for this problem i posted a separate threat here: