PIC18F25J50 MICROCHIP [Microchip Technology], PIC18F25J50 Datasheet - Page 412

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

PIC18F46J50 FAMILY
26.6
A unique feature on board the CTMU module is its
ability to generate system clock independent output
pulses, based on an external capacitor value. This is
accomplished using the internal comparator voltage
reference module, Comparator 2 input pin and an
external capacitor. The pulse is output onto the CTPLS
pin. To enable this mode, set the TGEN bit.
See
chosen by the user to determine the output pulse width
on CTPLS. The pulse width is calculated by
T = (C
source measurement step
Source
voltage (CV
FIGURE 26-4:
26.7
26.7.1
When the device enters any Sleep mode, the CTMU
module current source is always disabled. If the CTMU
is performing an operation that depends on the current
source when Sleep mode is invoked, the operation may
not
measurements may return erroneous values.
26.7.2
The behavior of the CTMU in Idle mode is determined
by the CTMUSIDL bit (CTMUCONH<5>). If CTMUSIDL
is cleared, the module will continue to operate in Idle
mode. If CTMUSIDL is set, the module’s current source
is disabled when the device enters Idle mode. If the
DS39931D-page 412
Figure 26-4
terminate
PULSE
Calibration”) and V is the internal reference
Creating a Delay with the CTMU
Module
Operation During Sleep/Idle
Modes
/I)*V, where I is known from the current
REF
SLEEP MODE AND DEEP SLEEP
MODES
IDLE MODE
).
correctly.
for an example circuit. C
TYPICAL CONNECTIONS AND INTERNAL CONFIGURATION FOR PULSE
DELAY GENERATION
C
CTED1
(Section 26.3.1 “Current
C2INB
PULSE
Capacitance
and
PULSE
EDG1
time
CV
is
Current Source
PIC18F46J50 Device
REF
Comparator
CTMU
C2
An example use of this feature is for interfacing with
variable capacitive-based sensors, such as a humidity
sensor. As the humidity varies, the pulse width output
on CTPLS will vary. The CTPLS output pin can be
connected to an input capture pin and the varying pulse
width is measured to determine the humidity in the
application.
Follow these steps to use this feature:
1.
2.
3.
4.
5.
module is performing an operation when Idle mode is
invoked, in this case, the results will be similar to those
with Sleep mode.
26.8
Upon Reset, all registers of the CTMU are cleared. This
leaves the CTMU module disabled, its current source is
turned off and all configuration options return to their
default settings. The module needs to be re-initialized
following any Reset.
If the CTMU is in the process of taking a measurement at
the time of Reset, the measurement will be lost. A partial
charge may exist on the circuit that was being measured,
and should be properly discharged before the CTMU
makes subsequent attempts to make a measurement.
The circuit is discharged by setting and then clearing the
IDISSEN bit (CTMUCONH<1>) while the A/D Converter
is connected to the appropriate channel.
Initialize Comparator 2 (with CPOL = 1).
Initialize the comparator voltage reference.
Initialize the CTMU and enable time delay
generation by setting the TGEN bit.
Set EDG1STAT.
When C
reference trip point, an output pulse is generated
on CTPLS.
Effects of a Reset on CTMU
PULSE
charges to the value of the voltage
CTPLS
 2011 Microchip Technology Inc.