SLEEP_MODE_PWR_DOWN Arduino Chip with Serial ATMEGA328P-PU

Hi,

I have the ATMega328P-PU (the CPU of the arduino) running on just the breadboard. I want to wake it up from a SLEEP_MODE_PWR_DOWN. I was looking through the data sheet
http://www.atmel.com/Images/doc8161.pdf

page 41 and it said I can use serial to wake it up. So does that mean an XBee can wake it using TX and RX pins? How do I wake the chip using serial?

Thanks
Kiwi

From Table 10-1, it appears you would have to enable a Pin Change Interrupt (PCINT) on the Rx pin to be able to wake from activity on the Rx pin.