Punkt3:
thanks for the hint.so far i connected only the data pin (connected to digital2) and ground pin to the Arduino.
At the moment the Arduino is powered via the usb connector.however if i tested the simple code for simulating the DS1990A - the Arduino (simulated DS1990A) is not listed in the bus list. =(
somehow i have no idea what i can do to get this setup work - but i know that it must work.
Markus got this running on an Arduino nano if i am not wrong...
Looks like I have some work to do!