Seemanta:

I know from your prior posting about your project that you are determined to make this parallel interface RTC work for you (oops I forgot - your sister). I do want to re-suggest the relative ease there is to connect up a PCF8563 RTC from NXP to an MCU. There are only 8-pins to deal with. And then you need a small coincell, a pencil lead crystal, a couple caps, two I2C bus resistors and a BAT54C package to OR the RTC VDD from the battery or the MCU supply.

If you look at this RTC's data sheet you will also note that the chip specs indicate that the limiting value for input voltages is -0.5V instead of the -0.3V that your sensitive parallel RTC has!!

I also believe that the 8-pin chip has a possibility of lasting longer on the same battery due to the fewer number of pins that represent possible leakage paths while the MCU section is shut down.

Michael Karas