saravananm92:
Do I have to enable the square wave output explicitly by program?(The datasheet says it all).
Yes you need to enable it in the control register. Bit 4 is SQWE (square wave enable) and bits 0-1 are the frequency required. For what you want bits 0 & 1 need to be cleared and bit 4 needs to be set. Any good RTC library will have functions to do this, what library are you using?