Real Time Clock Module
Description: This a custom designed module for the DS1307 Real Time Clock. The module comes fully assembled and pre-programmed with the current time (ok, so it's our current time - MST). The included Lithium coin cell battery (CR1225 41mAh) will run the module for a minimum of 9 years (17 years typical) without external 5V power. The DS1307 is accessed via the I2C protocol. We've written a test-bed to program the modules. This test-bed code should give you some insight on how to interface the module to any microcontroller using our example software I2C and BCD routines. Features: - Two wire I2C interface - Hour : Minutes : Seconds AM/PM - Day Month, Date - Year - Leap year compensation - Accurate calendar up to year 2100 - Battery backup included - 1Hz output pin - 56 Bytes of Non-volatile memory available to user Dimensions: 0.75x0.75" (20x20mm)
DS1307 Datasheet 
RTC-demo 