hi every one i am using 89s52 and the RTC DS 1307 i have done the all i2c interfacing the program. run very well as far as power is on ince the power down and agin power up output is not proper. on the RTC i did not get the frequency but 5 V supply 3V form battery even SCL and SDA also present showing all data tranmission when i change the RTC and again set all the RTC parameter date ,month ,year,hrs,minute,sec. it woking properly as far as power is on.as power is off problem arise again to over come this change the RTC and again setting the various parameter crystal used 32.768kHz. Control reg. 0x13 help me to solved this