DS1307-IC

The DS1307 serial real-time clock (RTC) is a lowpower, full binary-coded decimal (BCD) clock/calendar 
plus 56 bytes of NV SRAM. Address and data are 
transferred serially through an I2
C, bidirectional bus. 
The clock/calendar provides seconds, minutes, hours, 
day, date, month, and year information. The end of 
the month date is automatically adjusted for months 
with fewer than 31 days, including corrections for leap 
year. The clock operates in either the 24-hour or 12-
hour format with AM/PM indicator. The DS1307 has a 
built-in power-sense circuit that detects power failures 
and automatically switches to the backup supply. 
Timekeeping operation continues while the part 
operates from the backup supply.

Documents:

http://datasheets.maximintegrated.com/en/ds/DS1307.pdf