Yes, sim programs are expensive. I had a free beta-testversion once, it had still to much bugs to work with, after that came the pay-version.. I also like to life-test also my bankaccount.. it only takes sometimes some more time. But the good side is that when it workt it really works and with sim-programs is that always a question..

Well, Possibli can you tell me the length of a I2Cread/write procedure because I think that it is also to long. When I start the timer after the ISR it will only read the RTC, it never finishes the coldstart.

I did try to set the prescale to 1:16 but it hadn't any good progress. How do I become a timerinterrupt every 8mSec? of 16msec? Maby I can thy that so it works..