PIC18F25J11-I/PT MICROCHIP [Microchip Technology], PIC18F25J11-I/PT Datasheet - Page 383

• Manufacturer Part Number: PIC18F25J11-I/PT
• Description: 28/44-Pin, Low-Power, High-Performance Microcontrollers with nanoWatt XLP Technology
• Manufacturer: MICROCHIP [Microchip Technology]

24.5
Time can be precisely measured after the ratio (C/I) is
measured from the current and capacitance calibration
step by following these steps:
1.
2.
3.
4.
5.
FIGURE 24-3:
© 2009 Microchip Technology Inc.
Initialize the A/D Converter and the CTMU.
Set EDG1STAT.
Set EDG2STAT.
Perform an A/D conversion.
Calculate the time between edges as T = (C/I) * V,
where I is calculated in the current calibration step
(Section 24.3.1 “Current Source Calibration”),
C is calculated in the capacitance calibration step
(Section 24.3.2 “Capacitance Calibration”) and
V is measured by performing the A/D conversion.
Measuring Time with the CTMU
Module
TYPICAL CONNECTIONS AND INTERNAL CONFIGURATION FOR TIME
MEASUREMENT
CTEDG1
CTEDG2
AN
R
PR
X
EDG2
PIC18F46J11 Device
EDG1
C
AD
A/D Converter
Current Source
CTMU
PIC18F46J11 FAMILY
Output Pulse
It is assumed that the time measured is small enough
that the capacitance, C
to the A/D Converter. For the smallest time measure-
ment, always set the A/D Channel Select register
(AD1CHS) to an unused A/D channel; the correspond-
ing pin for which is not connected to any circuit board
trace. This minimizes added stray capacitance, keep-
ing 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.
OFFSET
, provides a valid voltage
DS39932C-page 383