first, thank you all for your helpful replys, especially kai klaas postings were helpful, a special thank to him! i've initialised the timer now but now i've the problem with saving the values of the Timer2.
The Cookbook says: When a recurring external event is represented in the form of rising or falling edges on one of the four capture pins, the time between two events can be measured usng Timer T2 and a capture registers.
In my case the capture pin is the pin CT0I. I've no idea how to measure the time now between 2 following square signals. i thought to save the value of CT0I on a register, eg.r7. But how can the difference be built now? please help me.

greetings



source code:
here the link to the code