Microchip Technology MCU PIC PIC18F87K22-I/PTRSL TQFP-80 MCP PIC18F87K22-I/PTRSL Data Sheet
Product codes
PIC18F87K22-I/PTRSL
PIC18F87K22 FAMILY
DS39960D-page 390
2009-2011 Microchip Technology Inc.
27.2.5
INTERRUPTS
The CTMU sets its interrupt flag (PIR3<3>) whenever
the current source is enabled, then disabled. An inter-
rupt is generated only if the corresponding interrupt
enable bit (PIE3<3>) is also set. If edge sequencing is
not enabled (i.e., Edge 1 must occur before Edge 2), it
is necessary to monitor the edge status bits and
determine which edge occurred last and caused the
interrupt.
the current source is enabled, then disabled. An inter-
rupt is generated only if the corresponding interrupt
enable bit (PIE3<3>) is also set. If edge sequencing is
not enabled (i.e., Edge 1 must occur before Edge 2), it
is necessary to monitor the edge status bits and
determine which edge occurred last and caused the
interrupt.
27.3
CTMU Module Initialization
The following sequence is a general guideline used to
initialize the CTMU module:
1.
initialize the CTMU module:
1.
Select the current source range using the
IRNGx bits (CTMUICON<1:0>).
IRNGx bits (CTMUICON<1:0>).
2.
Adjust the current source trim using the ITRIMx
bits (CTMUICON<7:2>).
bits (CTMUICON<7:2>).
3.
Configure the edge input sources for Edge 1 and
Edge 2 by setting the EDG1SEL and EDG2SEL
bits (CTMUCONL<3:2> and <6:5>, respectively).
Edge 2 by setting the EDG1SEL and EDG2SEL
bits (CTMUCONL<3:2> and <6:5>, respectively).
4.
Configure the input polarities for the edge inputs
using the EDG2POL and EDG1POL bits
(CTMUCONL<7,4>).
The default configuration is for negative edge
polarity (high-to-low transitions).
using the EDG2POL and EDG1POL bits
(CTMUCONL<7,4>).
The default configuration is for negative edge
polarity (high-to-low transitions).
5.
Enable edge sequencing using the EDGSEQEN
bit (CTMUCONH<2>).
By default, edge sequencing is disabled.
bit (CTMUCONH<2>).
By default, edge sequencing is disabled.
6.
Select the operating mode (Measurement or
Time Delay) with the TGEN bit.
The default mode is Time/Capacitance
Measurement.
Time Delay) with the TGEN bit.
The default mode is Time/Capacitance
Measurement.
7.
Configure the module to automatically trigger
an A/D conversion when the second edge
event has occurred, using the CTTRIG bit
(CTMUCONH<0>).
The conversion trigger is disabled by default.
an A/D conversion when the second edge
event has occurred, using the CTTRIG bit
(CTMUCONH<0>).
The conversion trigger is disabled by default.
8.
Discharge the connected circuit by setting the
IDISSEN bit (CTMUCONH<1>).
IDISSEN bit (CTMUCONH<1>).
9.
After waiting a sufficient time for the circuit to
discharge, clear IDISSEN.
discharge, clear IDISSEN.
10. Disable the module by clearing the CTMUEN bit
(CTMUCONH<7>).
11. Clear the Edge Status bits, EDG2STAT and
EDG1STAT (CTMUCONL<1:0>).
12. Enable both edge inputs by setting the EDGEN
bit (CTMUCONH<3>).
13. Enable the module by setting the CTMUEN bit.
Depending on the type of measurement or pulse
generation being performed, one or more additional
modules may also need to be initialized and configured
with the CTMU module:
• Edge Source Generation: In addition to the
generation being performed, one or more additional
modules may also need to be initialized and configured
with the CTMU module:
• Edge Source Generation: In addition to the
external edge input pins, CCPx Special Event
Triggers can be used as edge sources for the
CTMU.
Triggers can be used as edge sources for the
CTMU.
• Capacitance or Time Measurement: The CTMU
module uses the A/D Converter to measure the
voltage across a capacitor that is connected to one
of the analog input channels.
voltage across a capacitor that is connected to one
of the analog input channels.
• Pulse Generation: When generating system clock
independent, output pulses, the CTMU module
uses Comparator 2 and the associated
comparator voltage reference.
uses Comparator 2 and the associated
comparator voltage reference.
27.4
Calibrating the CTMU Module
The CTMU requires calibration for precise measure-
ments of capacitance and time, as well as for accurate
time delay. If the application only requires measurement
of a relative change in capacitance or time, calibration is
usually not necessary. An example of a less precise
application is a capacitive touch switch, in which the
touch circuit has a baseline capacitance and the added
capacitance of the human body changes the overall
capacitance of a circuit.
If actual capacitance or time measurement is required,
two hardware calibrations must take place:
• The current source needs calibration to set it to a
ments of capacitance and time, as well as for accurate
time delay. If the application only requires measurement
of a relative change in capacitance or time, calibration is
usually not necessary. An example of a less precise
application is a capacitive touch switch, in which the
touch circuit has a baseline capacitance and the added
capacitance of the human body changes the overall
capacitance of a circuit.
If actual capacitance or time measurement is required,
two hardware calibrations must take place:
• The current source needs calibration to set it to a
precise current.
• The circuit being measured needs calibration to
measure or nullify any capacitance other than that
to be measured.
to be measured.
27.4.1
CURRENT SOURCE CALIBRATION
The current source on board the CTMU module has a
range of ±60% nominal for each of three current
ranges. For precise measurements, it is possible to
measure and adjust this current source by placing a
high-precision resistor, R
range of ±60% nominal for each of three current
ranges. For precise measurements, it is possible to
measure and adjust this current source by placing a
high-precision resistor, R
CAL
, onto an unused analog
.
To measure the current source:
1.
1.
Initialize the A/D Converter.
2.
Initialize the CTMU.
3.
Enable the current source by setting EDG1STAT
(CTMUCONL<0>).
(CTMUCONL<0>).
4.
Issue the settling time delay.
5.
Perform the A/D conversion.
6.
Calculate the current source current using
I = V/R
I = V/R
CAL
, where R
CAL
is a high-precision
resistance and V is measured by performing an
A/D conversion.
A/D conversion.