John Boxall over at Tronixstuff has a series of Arduino tutorials. This chapter fifty-four of a series will show you how to use the NXP PCF8563 real-time clock IC with Arduino:
Recently a few people have been asking about the PCF8563 real-time clock IC from NXP – so this is a tutorial on how to use it for time, date, alarm clock and square-wave generation purposes.
The PCF8563 is another inexpensive RTC that can be used with an Arduino or other platforms due to the wide operating voltage (1 to 5.5V DC), I2C interface, and very low power consumption (when powered by a backup battery it only draws 0.25 μA).