Usually a real-time clock is done by either having a real-time clock module built in to the microcontroller, or to use an external real-time clock module such as the DS1305 from Maxim.

These can typically be programmed to trigger an interrupt at a pre-defined time, and run off their own 32.768KHz crystal.  They often have their own battery-backup circuit, and some even contain charge circuits too.

What would be the best way to design a real time clock for the MSP430?
What is it?

How is it performed?

May one perform it?

And, if so, when may it be used?
