En el manual de referencia aparece esto:
11.7 MEASURING TIME WITH THE CTMU MODULE
Time can be precisely measured after the ratio (C/I) is measured from the current and
capacitance calibration step by following these steps:
1. Initialize the A/D Converter and the CTMU.
2. Set EDG1STAT.
3. Set EDG2STAT.
4. Perform an A/D conversion.
5. Calculate the time between edges as T = (C/I) * V, where I is calculated in the current
calibration step (Section 11.5.1 ìCurrent Source Calibrationî), C is calculated in the
capacitance calibration step (Section 11.5.2 ìCapacitance Calibrationî) and V is
measured by performing the A/D conversion.
It is assumed that the time measured is small enough that the capacitance COFFSET provides a
valid voltage to the A/D Converter. For the smallest time measurement, always set the A/D Channel Select register (AD1CHS) to an unused A/D channel; the corresponding pin for which is not
connected to any circuit board trace. This minimizes added stray capacitance, keeping the total
circuit capacitance close to that of the A/D Converter itself (4-5 pF). To measure longer time intervals, an external capacitor may be connected to an A/D channel, and this channel selected when
making a time measurement.
Pero realmente creo que el CCP es más indicado para medir tiempos; si te animas y tienes dudas lo vemos.
