2 michael--> when i want to change the value of my RTC i first stop the RTC before writing the value. so this couldn't be the problem. but as you said in the marked part of the data sheet. i could be that i'm writing wrong value's to the RTC.

2 dennis--> i use the byte write operation with my I2C bus. but this couldn't be a problem i think.

after trying and trying, i finaly can
read the RTC. this isn't a problem any more. change day and month works fine, until i set the time to 23:59:59 and the date to 31-12-xx
every thing is alright except the year. the year doesn't get the right value. if i want to change the months or days (after chaging automaticly the year) the days and months count to 39 (by days) and 19 (by months). this only happens once. when i count back to a value between 1 and 31 (by days) and 1 and 12 (by months) everything is right again.
after changing the year. this problem happens once again.

this is very strange, does anyone have/ had this problem. and i hope that i explained my problem enough.