many thanks for your help. I did understand what you have suggested and the tmk_ExceptionHandler does no longer occur. I have one additional question. If I want to handle interrupts in a synchronous way without allowing nesting interrupts what do I need to do! I would like to have it in this ways that interrupts are queued one after each other and synchronous processed without nesting interrupts. What do I need to do for this? I have looked to the online help and into the BF561 but I could not find anything.