I have not designed the system, so I can only work on what I have got. So I have to use F-DIO and that is not going to change. Thank you for your advise. I posted here to get an answer for only one question - how often are F-DIO read in F-CPU. I got different answers, so I assume that nobody is sure how it works. Thanks anyway and you are right, we can close this topic.

hi again, 

have a look to the manual:

SIMATIC Industrial Software SIMATIC Safety - Configuring and Programming

In Chapter 5.1.2 you find the program structure of the Safety Program

You can also see that the Inputs read when the F-OB is called and the outputs written when the F-OB is ending.

regards,