PIC18F65K90T-I/PT Microchip Technology, PIC18F65K90T-I/PT Datasheet - Page 418

• Manufacturer Part Number: PIC18F65K90T-I/PT
• Description: 32kB Flash, 2kB RAM, 1kB EE, NanoWatt XLP, LCD 64 TQFP 10x10x1mm T/R
• Manufacturer: Microchip Technology
• Series: PIC® XLP™ 18Fr

Specifications of PIC18F65K90T-I/PT

• Processor Series: PIC18F
• Core: PIC
• Data Bus Width: 8 bit
• Program Memory Type: Flash
• Program Memory Size: 32 KB
• Data Ram Size: 2 KB
• Interface Type: I2C, SPI
• Maximum Clock Frequency: 64 MHz
• Number Of Timers: 8
• Operating Supply Voltage: 1.8 V to 5.5 V
• Maximum Operating Temperature: + 125 C
• 3rd Party Development Tools: 52715-96, 52716-328, 52717-734, 52712-325, EWPIC18
• Minimum Operating Temperature: - 40 C
• On-chip Adc: 12 bit, 16 Channel
• 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: 53
• Eeprom Size: 1K x 8
• Ram Size: 2K x 8
• Voltage - Supply (vcc/vdd): 1.8 V ~ 5.5 V
• Data Converters: A/D 16x12b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 64-TQFP
• Lead Free Status / Rohs Status: Details

PIC18F87K90 FAMILY
27.5
There are two ways to measure capacitance with the
CTMU. The absolute method measures the actual
capacitance value. The relative method only measures
for any change in the capacitance.
27.5.1
For absolute capacitance measurements, both the
current and capacitance calibration steps, found in
Section 27.4 “Calibrating the CTMU Module”
should be followed.
To perform these measurements:
1.
2.
3.
4.
5.
6.
7.
8.
DS39957D-page 418
Initialize the A/D Converter.
Initialize the CTMU.
Set EDG1STAT.
Wait for a fixed delay, T .
Clear EDG1STAT.
Perform an A/D conversion.
Calculate the total capacitance, C
where:
• I is known from the current source
• T is a fixed delay
• V is measured by performing an A/D
Subtract the stray and A/D capacitance
( C
Calibration”
measured capacitance.
measurement step (
Source Calibration”
conversion
OFFSET
Measuring Capacitance with the
CTMU
ABSOLUTE CAPACITANCE
MEASUREMENT
from
) from C
Section 27.4.2 “Capacitance
Section 27.4.1 “Current
TOTAL
)
to determine the
TOTAL
= (I * T)/V ,
,
measurements. When detecting a valid press of a
27.5.2
Not all applications require precise capacitance
capacitance-based switch, only a relative change of
capacitance needs to be detected.
In such an application, when the switch is open (or not
touched), the total capacitance is the capacitance of the
combination of the board traces, the A/D Converter and
other elements. A larger voltage will be measured by the
A/D Converter. When the switch is closed (or touched),
the total capacitance is larger due to the addition of the
capacitance of the human body to the above listed
capacitances and a smaller voltage will be measured by
the A/D Converter.
To detect capacitance changes simply:
1.
2.
3.
4.
5.
The voltage measured by performing the A/D conver-
sion is an indication of the relative capacitance. In this
case, no calibration of the current source or circuit
capacitance measurement is needed. (For a sample
software routine for a capacitive touch switch, see
Example
Initialize the A/D Converter and the CTMU.
Set EDG1STAT.
Wait for a fixed delay.
Clear EDG1STAT.
Perform an A/D conversion.
27-4.)
RELATIVE CHARGE
MEASUREMENT
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