PIC18F24J11 MICROCHIP [Microchip Technology], PIC18F24J11 Datasheet - Page 389

• Manufacturer Part Number: PIC18F24J11
• Description: 28/44-Pin, Low-Power, High-Performance USB Microcontrollers with nanoWatt XLP Technology
• Manufacturer: MICROCHIP [Microchip Technology]

25.5
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 25-3:
 2011 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 25.3.1 “Current Source
C is calculated in the capacitance calibration step
(Section 25.3.2 “Capacitance
V is measured by performing the A/D conversion.
Measuring Time with the CTMU
Module
TYPICAL CONNECTIONS AND INTERNAL CONFIGURATION FOR TIME
MEASUREMENT
Calibration”) and
CTED1
CTED2
Calibration”),
AN
C
EXT
X
EDG2
EDG1
PIC18F46J11 FAMILY
C
It is assumed that the time measured is small enough
that the capacitance, C
age to the A/D Converter. For the smallest time mea-
surement, 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.
AD
A/D Converter
PIC18F46J11
Current Source
CTMU
AD
+ C
EXT
, provides a valid volt-
DS39932D-page 389