Microchip Technology ARD00385 Data Sheet

 2009-2011 Microchip Technology Inc.

DS39957D-page 407

The Charge Time Measurement Unit (CTMU) is a
flexible analog module that provides accurate differen-
tial time measurement between pulse sources, as well
as asynchronous pulse generation. By working with
other on-chip analog modules, the CTMU can precisely
measure time, capacitance and relative changes in
capacitance or generate output pulses with a specific
time delay. The CTMU is ideal for interfacing with
capacitive-based sensors.
The module includes these key features:
• Up to 24 channels available for capacitive or time 

measurement input

• On-chip precision current source
• Four-edge input trigger sources
• Polarity control for each edge source
• Control of edge sequence

• Control of response to edges
• Time measurement resolution of 1 nanosecond
• High-precision time measurement
• Time delay of external or internal signal 

asynchronous to system clock

• Accurate current source suitable for capacitive 

measurement

The CTMU works in conjunction with the A/D Converter
to provide up to 24 channels for time or charge
measurement, depending on the specific device and
the number of A/D channels available. When config-
ured for time delay, the CTMU is connected to one of
the analog comparators. The level-sensitive input edge
sources can be selected from four sources: two
external inputs or the ECCP1/ECCP2 Special Event
Triggers.
The CTMU special event can trigger the Analog-to-Digital
Converter module.

 provides a block diagram of the CTMU.

CTED1

CTED2

Current Source

Edge

Control

Logic

CTMUCON

Pulse

Generator

A/D Converter

Comparator 2
Input

ECCP2

ECCP1

Current

Control

ITRIM<5:0>
IRNG<1:0>

CTMUICON

CTMU

Control

Logic

EDGEN
EDGSEQEN
EDG1SELx
EDG1POL
EDG2SELx
EDG2POL

EDG1STAT
EDG2STAT

TGEN

IDISSEN
CTTRIG

A/D Trigger

CTPLS

Comparator 2 Output