PIC18F85K22-I/PT Microchip Technology, PIC18F85K22-I/PT Datasheet - Page 396

• Manufacturer Part Number: PIC18F85K22-I/PT
• Description: IC, 8BIT MCU, PIC18F, 64MHZ, TQFP-80
• Manufacturer: Microchip Technology
• Series: PIC® XLP™ 18Fr

Specifications of PIC18F85K22-I/PT

• Controller Family/series: PIC18
• No. Of I/o's: 69
• Eeprom Memory Size: 1KB
• Ram Memory Size: 2KB
• Cpu Speed: 64MHz
• No. Of Timers: 8
• Core Size: 8 Bit
• Program Memory Size: 32KB
• Core Processor: PIC
• Speed: 64MHz
• Connectivity: EBI/EMI, I²C, LIN, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, LVD, POR, PWM, WDT
• Number Of I /o: 69
• Program Memory Type: FLASH
• Eeprom Size: 1K x 8
• Ram Size: 2K x 8
• Voltage - Supply (vcc/vdd): 1.8 V ~ 5.5 V
• Data Converters: A/D 24x12b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 80-TQFP
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

PIC18F87K22 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”
be followed.
To perform these measurements:
1.
2.
3.
4.
5.
6.
7.
8.
DS39960D-page 396
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 conversion
Subtract the stray and A/D capacitance
( C
Calibration”
measured capacitance.
measurement step (
Source Calibration”
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 ,
should
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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