PIC18F46K80T-I/SP 查看數據表（PDF） - Microchip Technology

零件编号

产品描述 (功能)

生产厂家

PIC18F46K80T-I/SP

28/40/44/64-Pin, Enhanced Flash Microcontrollers with ECAN™ and nanoWatt XLP Technology

Microchip Technology 

PIC18F66K80 FAMILY

18.6 Measuring Time with the CTMU

Module

Time can be precisely measured after the ratio (C/I) is

measured from the current and capacitance calibration

step. To do that:

1. Initialize the A/D Converter and the CTMU.

2. Set EDG1STAT.

3. Set EDG2STAT.

4. Perform an A/D conversion.

5. Calculate the time between edges as T = (C/I) * V,

where:

• I is calculated in the current calibration

step (Section 18.4.1 “Current Source

Calibration”)

• C is calculated in the capacitance calibra-

tion step (Section 18.4.2 “Capacitance

Calibration”)

• V is measured by performing the A/D conversion

It is assumed that the time measured is small enough

that the capacitance, CAD + CEXT, provides a valid

voltage to the A/D Converter. For the smallest time

measurement, always set the A/D Channel Select bits

CHS<4:0> (ADCON0<6:2>) to an unused A/D channel,

the corresponding pin for which is not connected to any

circuit board trace. This minimizes added stray capaci-

tance, keeping the total circuit capacitance close to that

of the A/D Converter itself (25 pF).

To measure longer time intervals, an external capacitor

may be connected to an A/D channel and that channel

selected whenever making a time measurement.

FIGURE 18-3:

TYPICAL CONNECTIONS AND INTERNAL CONFIGURATION FOR TIME

MEASUREMENT

CTED1

CTED2

ANX

CEXT

PIC18F66K80

CTMU

EDG1 Current Source

EDG2

A/D Voltage

A/D Converter

CAD

DS39977F-page 248

 2010-2012 Microchip Technology Inc.

Share Link: