Microchip Technology MA240017 Ficha De Dados

DS39927C-page 190

 2008-2011 Microchip Technology Inc.

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.

 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.

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, CV

REF

, 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 CV

REF

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.

 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”

.

A/D Converter

CTMU

CTED1

CTED2

ANx

Output Pulse 

EDG1

EDG2

C

AD

R

PR

Current Source

C2

CV

REF

CTPLS

Current Source

Comparator

CTMU

CTED1

C2INB

C

DELAY

EDG1

-