PIC18F25J50 MICROCHIP [Microchip Technology], PIC18F25J50 Datasheet - Page 411

• Manufacturer Part Number: PIC18F25J50
• Description: 28/44-Pin, Low-Power, High-Performance USB Microcontrollers with nanoWatt XLP Technology
• Manufacturer: MICROCHIP [Microchip Technology]

26.5
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 26-3:
 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 26.3.1 “Current Source
C is calculated in the capacitance calibration step
(Section 26.3.2 “Capacitance
V is measured by performing the A/D conversion.
Measuring Time with the CTMU
Module
TYPICAL CONNECTIONS AND INTERNAL CONFIGURATION FOR TIME
MEASUREMENT
CTED1
CTED2
C
AN
EXT
X
Calibration”) and
Calibration”),
EDG2
PIC18F46J50 Device
EDG1
C
AD
A/D Converter
Current Source
CTMU
PIC18F46J50 FAMILY
A/D Voltage
It is assumed that the time measured is small enough
that the capacitance, C
age to the A/D Converter. For the smallest time
measurement, always set the A/D Channel Select reg-
ister (AD1CHS) to an unused A/D channel; the
corresponding pin 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. 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
+ C
EXT
, provides a valid volt-
DS39931D-page 411