If you have a spare timer register, its even simpler and you dont have to waste any code and time on that.

Program the /INT(n) line as external timer control for Timer(n) and apply a standard signal of sufficient frequency to T(n) pin of the timer.

For example, you can use a 40 KHz signal that will have a least count of 25 uSecs (period of the signal) Reset the timer will count before you start the count and stop the timer as soon as the signal on INT line drops. The count in the counter registers is number of 25 uS units the pulse had lasted. Once can easily decide a suitable frequnecy for optimum resolution and conversion routines that asa far as posible do not require heavy calculations.

girish