參數(shù)資料
型號: ATMEGA649V-8MI
廠商: Atmel
文件頁數(shù): 83/146頁
文件大?。?/td> 0K
描述: IC AVR MCU FLASH 64K 1.8V 64QFN
產(chǎn)品培訓(xùn)模塊: megaAVR Introduction
標(biāo)準(zhǔn)包裝: 260
系列: AVR® ATmega
核心處理器: AVR
芯體尺寸: 8-位
速度: 8MHz
連通性: SPI,UART/USART,USI
外圍設(shè)備: 欠壓檢測/復(fù)位,LCD,POR,PWM,WDT
輸入/輸出數(shù): 53
程序存儲器容量: 64KB(32K x 16)
程序存儲器類型: 閃存
EEPROM 大小: 2K x 8
RAM 容量: 4K x 8
電壓 - 電源 (Vcc/Vdd): 1.8 V ~ 5.5 V
數(shù)據(jù)轉(zhuǎn)換器: A/D 8x10b
振蕩器型: 內(nèi)部
工作溫度: -40°C ~ 85°C
封裝/外殼: 64-VFQFN 裸露焊盤
包裝: 托盤
2010-2012 Microchip Technology Inc.
DS41440C-page 325
PIC16(L)F1825/1829
27.5
Timer Resources
To measure the change in frequency of the capacitive
sensing oscillator, a fixed time base is required. For the
period of the fixed time base, the capacitive sensing
oscillator is used to clock either Timer0 or Timer1. The
frequency of the capacitive sensing oscillator is equal
to the number of counts in the timer divided by the
period of the fixed time base.
27.6
Fixed Time Base
To measure the frequency of the capacitive sensing
oscillator, a fixed time base is required. Any timer
resource or software loop can be used to establish the
fixed time base. It is up to the end user to determine the
method in which the fixed time base is generated.
27.6.1
TIMER0
To select Timer0 as the timer resource for the CPS
module:
Set the T0XCS bit of the CPSCON0 register.
Clear the TMR0CS bit of the OPTION_REG
register.
When Timer0 is chosen as the timer resource, the
capacitive sensing oscillator will be the clock source for
additional information.
27.6.2
TIMER1
To select Timer1 as the timer resource for the CPS
module, set the TMR1CS<1:0> of the T1CON register
to ‘11’. When Timer1 is chosen as the timer resource,
the capacitive sensing oscillator will be the clock
source for Timer1. Because the Timer1 module has a
gate control, developing a time base for the frequency
measurement can be simplified by using the Timer0
overflow flag.
It is recommend that the Timer0 overflow flag, in con-
junction with the Toggle mode of the Timer1 Gate, be
used to develop the fixed time base required by the
software portion of the CPS module. Refer to
for
additional information.
TABLE 27-2:
TIMER1 ENABLE FUNCTION
27.7
Software Control
The software portion of the CPS module is required to
determine the change in frequency of the capacitive
sensing oscillator. This is accomplished by the
following:
Setting a fixed time base to acquire counts on
Timer0 or Timer1.
Establishing the nominal frequency for the
capacitive sensing oscillator.
Establishing the reduced frequency for the
capacitive sensing oscillator due to an additional
capacitive load.
Set the frequency threshold.
27.7.1
NOMINAL FREQUENCY
(NO CAPACITIVE LOAD)
To determine the nominal frequency of the capacitive
sensing oscillator:
Remove any extra capacitive load on the selected
CPSx pin.
At the start of the fixed time base, clear the timer
resource.
At the end of the fixed time base save the value in
the timer resource.
The value of the timer resource is the number of
oscillations of the capacitive sensing oscillator for the
given time base. The frequency of the capacitive
sensing oscillator is equal to the number of counts on
in the timer divided by the period of the fixed time base.
27.7.2
REDUCED FREQUENCY
(ADDITIONAL CAPACITIVE LOAD)
The extra capacitive load will cause the frequency of the
capacitive sensing oscillator to decrease. To determine
the reduced frequency of the capacitive sensing
oscillator:
Add a typical capacitive load on the selected
CPSx pin.
Use the same fixed time base as the nominal
frequency measurement.
At the start of the fixed time base, clear the timer
resource.
At the end of the fixed time base save the value in
the timer resource.
The value of the timer resource is the number of
oscillations of the capacitive sensing oscillator with an
additional capacitive load. The frequency of the
capacitive sensing oscillator is equal to the number of
counts on in the timer divided by the period of the fixed
time base. This frequency should be less than the
value
obtained
during
the
nominal
frequency
measurement.
Note:
The fixed time base can not be generated
by the timer resource that the capacitive
sensing oscillator is clocking.
TMR1ON
TMR1GE
Timer1 Operation
00
Off
01
Off
10
On
11
Count Enabled by input
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