Here is a PLVD interrupt example that was done with that chip.

http://www.picbasic.co.uk/forum/showthread.php?t=6927

Darrell Taylor Interrupts here: http://darreltaylor.com/DT_INTS-14/intro.html

Darrell has included a HLVD_INT -- High/Low Voltage Detect in his interrupt rountines, but it needs a pic18 device.

http://darreltaylor.com/DT_INTS-18/home.html