Nitin,

Consider running at 3 volts, using a 1.842 MHz xtal.

After INIT, enter idle, when an interrupt occurs you "fall thru to a polling loop which interrogates state flags (set by the interrupt service routines) to determine what work is to be done, then re-enter idle.

Coding of the Interrupt Service routines requires some thought and should be short.

Don't forget use of a Timer interrupt allows the creation of very power efficient approaches to doing work while allowing the micro duty cycle to favor low power.

Also run the serial port with Transmit Interrupts.

regards,
p