jremington:
I suggest to use a standard I2C RTC module like the DS1307 or (much better) DS3231.These are readily available and are what most people use, so there is much more help available if you run into trouble.
yeah I heard that... I have already ordered DS3231. But shipping to my country sometimes takes more than 1 month so I thought to play around with DS1302 while waiting because it's the only module what local store can offer.