PIC18F27J53T-I/SO Microchip Technology, PIC18F27J53T-I/SO Datasheet - Page 433

• Manufacturer Part Number: PIC18F27J53T-I/SO
• Description: 28-pin, USB, 128KB Flash, 4KB RAM, 12 MIPS, 12-bit ADC, NanoWatt XLP 28 SOIC .30
• Manufacturer: Microchip Technology
• Series: PIC® XLP™ 18Fr

Specifications of PIC18F27J53T-I/SO

• Core Processor: PIC
• Core Size: 8-Bit
• Speed: 48MHz
• Connectivity: I²C, LIN, SPI, UART/USART, USB
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 22
• Program Memory Size: 128KB (64K x 16)
• Program Memory Type: FLASH
• Ram Size: 3.8K x 8
• Voltage - Supply (vcc/vdd): 2.15 V ~ 3.6 V
• Data Converters: A/D 10x10b/12b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: *
• Processor Series: PIC18F
• Core: PIC
• Data Bus Width: 8 bit
• Data Ram Size: 3.8 KB
• Interface Type: I2C, SPI, USART
• Maximum Clock Frequency: 48 MHz
• Number Of Programmable I/os: 16
• Number Of Timers: 8
• Operating Supply Voltage: 2.15 V to 3.6 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Eeprom Size: -
• Lead Free Status / Rohs Status: Details

27.4
There are two separate methods of measuring capaci-
tance with the CTMU. The first is the absolute method,
in which the actual capacitance value is desired. The
second is the relative method, in which the actual
capacitance is not needed, rather an indication of a
change in capacitance is required.
27.4.1
For absolute capacitance measurements, both the
current and capacitance calibration steps found in
Section 27.3 “Calibrating the CTMU Module”
should be followed. Capacitance measurements are
then performed using the following steps:
1.
2.
3.
4.
5.
6.
7.
8.
 2010 Microchip Technology Inc.
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
measurement step (see Section 27.3.1 “Current
Source Calibration”), T is a fixed delay and V is
measured by performing an A/D conversion.
Subtract the stray and A/D capacitance
(C
Calibration”) from C
measured capacitance.
OFFSET
Measuring Capacitance with the
CTMU
ABSOLUTE CAPACITANCE
MEASUREMENT
from Section 27.3.2 “Capacitance
TOTAL
to determine the
TOTAL
= (I * T)/V,
Preliminary
PIC18F47J53 FAMILY
27.4.2
An application may not require precise capacitance
measurements. For example, when detecting a valid
press of a capacitance-based switch, detecting a rela-
tive change of capacitance is of interest. In this type of
application, when the switch is open (or not touched),
the total capacitance is the capacitance of the combina-
tion of the board traces, the A/D Converter, etc. A larger
voltage will be measured by the A/D Converter. When
the switch is closed (or is 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.
Detecting capacitance changes is easily accomplished
with the CTMU using these steps:
1.
2.
3.
4.
5.
The voltage measured by performing the A/D conver-
sion is an indication of the relative capacitance. Note
that in this case, no calibration of the current source or
circuit capacitance measurement is needed. See
Example 27-4 for a sample software routine for a
capacitive touch switch.
Initialize the A/D Converter and the CTMU.
Set EDG1STAT.
Wait for a fixed delay.
Clear EDG1STAT.
Perform an A/D conversion.
RELATIVE CHARGE
MEASUREMENT
DS39964B-page 433