Hi,
I guess what you want is one pulse every 4.32s, in other words a frequency of 0.2315Hz.

Code:
'Produce squarewave on PortB.0 period~4.32s, 50% dutycycle.

Loop var Word

Main:
 High PortB.0
 For Loop = 0 to 2160       'Loop here for ~2.16s, tweak to match.   
   PauseUs 1000
 Next
 Low PortB.0
 For Loop = 0 to 2160       'Loop here for ~2.16s, tweak to match. 
   PauseUs 1000
 Next
Goto Main
Since the Pause statement in the For-Next loop is shorter (1mS) than what your interrupt period is (65mS) the ISR will still run.

However, your time-keeping will not be very accurate. You're only getting 983mS each second, give or take, 65536uS * 15 = 983040uS.

/Henrik Olsson.