Microchip Technology MA240017 Data Sheet
2008-2011 Microchip Technology Inc.
DS39927C-page 189
PIC24F16KA102 FAMILY
25.0
CHARGE TIME
MEASUREMENT UNIT (CTMU)
MEASUREMENT UNIT (CTMU)
The Charge Time Measurement Unit (CTMU) is a
flexible analog module that provides charge measure-
ment, accurate differential time measurement between
pulse sources and asynchronous pulse generation. Its
key features include:
• Four-edge input trigger sources
• Polarity control for each edge source
• Control of edge sequence
• Control of response to edges
• Time measurement resolution of one nanosecond
• Accurate current source suitable for capacitive
flexible analog module that provides charge measure-
ment, accurate differential time measurement between
pulse sources and asynchronous pulse generation. Its
key features include:
• Four-edge input trigger sources
• Polarity control for each edge source
• Control of edge sequence
• Control of response to edges
• Time measurement resolution of one nanosecond
• Accurate current source suitable for capacitive
measurement
Together with other on-chip analog modules, the CTMU
can be used to precisely measure time, measure
capacitance, measure relative changes in capacitance,
or generate output pulses that are independent of the
system clock. The CTMU module is ideal for interfacing
with capacitive-based touch sensors.
The CTMU is controlled through two registers:
CTMUCON and CTMUICON. CTMUCON enables the
module, and controls edge source selection, edge
can be used to precisely measure time, measure
capacitance, measure relative changes in capacitance,
or generate output pulses that are independent of the
system clock. The CTMU module is ideal for interfacing
with capacitive-based touch sensors.
The CTMU is controlled through two registers:
CTMUCON and CTMUICON. CTMUCON enables the
module, and controls edge source selection, edge
source polarity selection, and edge sequencing. The
CTMUICON register selects the current range of
current source and trims the current.
CTMUICON register selects the current range of
current source and trims the current.
25.1
Measuring Capacitance
The CTMU module measures capacitance by
generating an output pulse with a width equal to the
time between edge events on two separate input chan-
nels. The pulse edge events to both input channels can
be selected from four sources: two internal peripheral
modules (OC1 and Timer1) and two external pins
(CTED1 and CTED2). This pulse is used with the mod-
ule’s precision current source to calculate capacitance
according to the relationship:
generating an output pulse with a width equal to the
time between edge events on two separate input chan-
nels. The pulse edge events to both input channels can
be selected from four sources: two internal peripheral
modules (OC1 and Timer1) and two external pins
(CTED1 and CTED2). This pulse is used with the mod-
ule’s precision current source to calculate capacitance
according to the relationship:
For capacitance measurements, the A/D Converter
samples an external capacitor (C
samples an external capacitor (C
APP
) on one of its
input channels, after the CTMU output’s pulse. A
precision resistor (R
precision resistor (R
PR
) provides current source
calibration on a second A/D channel. After the pulse
ends, the converter determines the voltage on the
capacitor. The actual calculation of capacitance is
performed in software by the application.
ends, the converter determines the voltage on the
capacitor. The actual calculation of capacitance is
performed in software by the application.
capacitance measurements, and how the CTMU and
A/D modules are related in this application. This example
also shows the edge events coming from Timer1, but
other configurations using external edge sources are
possible. A detailed discussion on measuring capaci-
tance and time with the CTMU module is provided in the
“PIC24F Family Reference Manual”.
A/D modules are related in this application. This example
also shows the edge events coming from Timer1, but
other configurations using external edge sources are
possible. A detailed discussion on measuring capaci-
tance and time with the CTMU module is provided in the
“PIC24F Family Reference Manual”.
FIGURE 25-1:
TYPICAL CONNECTIONS AND INTERNAL CONFIGURATION FOR
CAPACITANCE MEASUREMENT
CAPACITANCE MEASUREMENT
Note:
This data sheet summarizes the features of
this group of PIC24F devices. It is not
intended to be a comprehensive reference
source. For more information on the
Charge Measurement Unit, refer to the
“PIC24F Family Reference Manual”
this group of PIC24F devices. It is not
intended to be a comprehensive reference
source. For more information on the
Charge Measurement Unit, refer to the
“PIC24F Family Reference Manual”
,
Section 11. “Charge Time Measurement
Unit (CTMU)”
Unit (CTMU)”
(DS39724).
I = C •
dV
dT
dT
PIC24F Device
A/D Converter
CTMU
ANx
C
APP
Output Pulse
EDG1
EDG2
R
PR
AN
Y
Timer1
Current Source