PIC24F16KA102 datasheet(188/254 Pages) MICROCHIP

188 / 254 page

PIC24F16KA102 FAMILY

DS39927B-page 186

Preliminary

25.2

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 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

CTEDG 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 (CDELAY) is connected to

the Comparator 2 pin, C2INB, and the comparator

voltage reference, CVREF, is connected to C2INA.

CVREF is then configured for a specific trip point. The

module begins to charge CDELAY when an edge event

is detected. When CDELAY charges above the CVREF

trip point, a pulse is output on CTPLS. The length of the

pulse delay is determined by the value of CDELAY and

the CVREF trip point.

Figure 25-3 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 “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

CTEDG1

CTEDG2

ANx

Output Pulse

EDG1

EDG2

CAD

RPR

Current Source

CVREF

CTPLS

PIC24F Device

Current Source

Comparator

CTMU

CTEDG1

C2INB

CDELAY

EDG1

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