PIC18F25K80 MICROCHIP [Microchip Technology], PIC18F25K80 Datasheet - Page 254

• Manufacturer Part Number: PIC18F25K80
• Manufacturer: MICROCHIP [Microchip Technology]

PIC18F66K80 FAMILY
18.6
Time can be precisely measured after the ratio ( C/I ) is
measured from the current and capacitance calibration
step. To do that:
1.
2.
3.
4.
5.
FIGURE 18-3:
DS39977C-page 254
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
• C is calculated in the capacitance calibra-
• V is measured by performing the A/D conversion
step ( Section 18.4.1 “Current Source
Calibration” )
tion step ( Section 18.4.2 “Capacitance
Calibration” )
Measuring Time with the CTMU
Module
TYPICAL CONNECTIONS AND INTERNAL CONFIGURATION FOR TIME
MEASUREMENT
CTED1
CTED2
AN
C
EXT
X
Preliminary
EDG2
EDG1
It is assumed that the time measured is small enough
that the capacitance, C
voltage to the A/D Converter. For the smallest time
measurement, always set the A/D Channel Select bits
CHS<4:0> (ADCON0<6:2>) to an unused A/D channel,
the corresponding pin for which is not connected to any
circuit board trace. This minimizes added stray capaci-
tance, keeping the total circuit capacitance close to that
of the A/D Converter itself (25 pF).
To measure longer time intervals, an external capacitor
may be connected to an A/D channel and that channel
selected whenever making a time measurement.
C
AD
A/D Converter
PIC18F66K80
Current Source
CTMU
A/D Voltage
 2011 Microchip Technology Inc.
AD
+ C
EXT
, provides a valid