Datasheet

PIC24F16KA102 FAMILY
DS39927C-page 190  2008-2011 Microchip Technology Inc.
25.2 Measuring Time
Time measurements on the pulse width can be similarly
performed using the A/D module’s internal capacitor
(C
AD) and a precision resistor for current calibration.
Figure 25-2 displays 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
CTED pins, but other configurations using internal
edge sources are possible.
25.3 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
voltage reference, CVREF, is connected to C2INA.
CV
REF 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 25-3 shows the external connections for pulse
generation, as well as the relationship of the different
analog modules required. While CTED1 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 “PIC24F Family Reference
Manual”.
FIGURE 25-2: TYPICAL CONNECTIONS AND INTERNAL CONFIGURATION FOR
TIME MEASUREMENT
FIGURE 25-3: TYPICAL CONNECTIONS AND INTERNAL CONFIGURATION FOR
PULSE DELAY GENERATION
PIC24F Device
A/D Converter
CTMU
CTED1
CTED2
ANx
Output Pulse
EDG1
EDG2
CAD
RPR
Current Source
C2
CVREF
CTPLS
PIC24F Device
Current Source
Comparator
CTMU
CTED1
C2INB
CDELAY
EDG1
-