Datasheet

PIC24FJ256GA110 FAMILY
DS30009905F-page 244  2007-2019 Microchip Technology Inc.
24.2 Measuring Time
Time measurements on the pulse width can be similarly
performed using the A/D module’s internal capacitor
(CAD) and a precision resistor for current calibration.
Figure 24-2 shows the external connections used for time
measurements, and how the CTMU and A/D modules are
related in this application. This example also shows both
edge events coming from the external CTEDG pins, but
other configurations using internal edge sources are pos-
sible. A detailed discussion on measuring capacitance
and time with the CTMU module is provided in the
“dsPIC33/PIC24 Family Reference Manual”.
24.3 Pulse Generation and Delay
The CTMU module can also generate an output pulse
with edges that are not synchronous with the device’s
system clock. More specifically, it can generate a pulse
with a programmable delay from an edge event input to
the module.
When the module is configured for pulse generation
delay by setting the TGEN bit (CTMUCON[12]), the
internal current source is connected to the B input of
Comparator 2. A capacitor (C
DELAY) is connected to
the Comparator 2 pin, C2INB, and the comparator volt-
age reference, CVREF, is connected to C2INA. CVREF
is then configured for a specific trip point. The module
begins to charge C
DELAY when an edge event is
detected. When C
DELAY charges above the CVREF trip
point, a pulse is output on CTPLS. The length of the
pulse delay is determined by the value of C
DELAY and
the CV
REF trip point.
Figure 24-3 shows the external connections for pulse
generation, as well as the relationship of the different
analog modules required. While CTEDG1 is shown as
the input pulse source, other options are available. A
detailed discussion on pulse generation with the CTMU
module is provided in the “dsPIC33/PIC24 Family
Reference Manual”.
FIGURE 24-2: TYPICAL CONNECTIONS AND INTERNAL CONFIGURATION FOR TIME
MEASUREMENT
FIGURE 24-3: TYPICAL CONNECTIONS AND INTERNAL CONFIGURATION FOR PULSE
DELAY GENERATION
PIC24FJ Device
A/D Converter
CTMU
CTEDG1
CTEDG2
ANx
Output Pulse
EDG1
EDG2
CAD
RPR
Current Source
C2
CVREF
CTPLS
PIC24FJ Device
Current Source
Comparator
CTMU
CTEDG1
C2INB
CDELAY
EDG1