PIC18F87K90-E/PT Microchip Technology, PIC18F87K90-E/PT Datasheet - Page 420

• Manufacturer Part Number: PIC18F87K90-E/PT
• Description: 128kB Flash, 4kB RAM, 1kB EE, 16MIPS, NanoWatt XLP, LCD, 5V 80 TQFP 12x12x1mm TR
• Manufacturer: Microchip Technology
• Series: PIC® XLP™ 18Fr

Specifications of PIC18F87K90-E/PT

• Core Processor: PIC
• Core Size: 8-Bit
• Speed: 64MHz
• Connectivity: I²C, LIN, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, LCD, POR, PWM, WDT
• Number Of I /o: 69
• Program Memory Size: 128KB (64K x 16)
• Program Memory Type: FLASH
• Eeprom Size: 1K x 8
• Ram Size: 4K x 8
• Voltage - Supply (vcc/vdd): 1.8 V ~ 5.5 V
• Data Converters: A/D 24x12b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 125°C
• Package / Case: 80-TQFP
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

PIC18F87K90 FAMILY
27.6
Time can be precisely measured after the ratio ( C/I ) is
measured from the current and capacitance calibration
step. To do that:
1.
2.
3.
4.
5.
FIGURE 27-3:
DS39957D-page 420
Initialize the A/D Converter and the CTMU.
Set EDG1STAT.
Set EDG2STAT.
Perform an A/D conversion.
Calculate the time between edges as T = (C/I) • V ,
where:
• I is calculated in the current calibration step
• C is calculated in the capacitance calibration step
• V is measured by performing the A/D conversion
(
(
Section 27.4.1 “Current Source Calibration”
Section 27.4.2 “Capacitance Calibration”
Measuring Time with the CTMU
Module
TYPICAL CONNECTIONS AND INTERNAL CONFIGURATION FOR TIME
MEASUREMENT
CTED1
CTED2
AN
R
PR
X
)
)
EDG1
EDG2
It is assumed that the time measured is small enough
that the capacitance, C
to the A/D Converter. For the smallest time measure-
ment, always set the A/D Channel Select register
(AD1CHS) to an unused A/D channel, the correspond-
ing pin for which is not connected to any circuit board
trace. This minimizes added stray capacitance,
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.
C
AD
PIC18F87K90
A/D Converter
Current Source
CTMU
Output Pulse
 2009-2011 Microchip Technology Inc.
OFFSET
, provides a valid voltage