参数资料
型号: PIC18F6620-E/PT
厂商: Microchip Technology
文件页数: 87/165页
文件大小: 0K
描述: IC PIC MCU FLASH 32KX16 64TQFP
产品培训模块: Asynchronous Stimulus
标准包装: 160
系列: PIC® 18F
核心处理器: PIC
芯体尺寸: 8-位
速度: 25MHz
连通性: I²C,SPI,UART/USART
外围设备: 欠压检测/复位,LVD,POR,PWM,WDT
输入/输出数: 52
程序存储器容量: 64KB(32K x 16)
程序存储器类型: 闪存
EEPROM 大小: 1K x 8
RAM 容量: 3.75K x 8
电压 - 电源 (Vcc/Vdd): 4.2 V ~ 5.5 V
数据转换器: A/D 12x10b
振荡器型: 外部
工作温度: -40°C ~ 125°C
封装/外壳: 64-TQFP
包装: 托盘
PIC18F6520/8520/6620/8620/6720/8720
DS39609B-page 26
2004 Microchip Technology Inc.
2.6.2
OSCILLATOR TRANSITIONS
PIC18FXX20 devices contain circuitry to prevent
“glitches” when switching between oscillator sources.
Essentially, the circuitry waits for eight rising edges of
the clock source that the processor is switching to. This
ensures that the new clock source is stable and that its
pulse width will not be less than the shortest pulse
width of the two clock sources.
A timing diagram indicating the transition from the main
oscillator to the Timer1 oscillator is shown in Figure 2-8.
The Timer1 oscillator is assumed to be running all the
time. After the SCS bit is set, the processor is frozen at
the next occurring Q1 cycle. After eight synchronization
cycles are counted from the Timer1 oscillator, operation
resumes. No additional delays are required after the
synchronization cycles.
FIGURE 2-8:
TIMING DIAGRAM FOR TRANSITION FROM OSC1 TO TIMER1 OSCILLATOR
The sequence of events that takes place when switch-
ing from the Timer1 oscillator to the main oscillator will
depend on the mode of the main oscillator. In addition
to eight clock cycles of the main oscillator, additional
delays may take place.
If the main oscillator is configured for an external
crystal (HS, XT, LP), then the transition will take place
after an oscillator start-up time (TOST) has occurred. A
timing diagram, indicating the transition from the
Timer1 oscillator to the main oscillator for HS, XT and
LP modes, is shown in Figure 2-9.
FIGURE 2-9:
TIMING FOR TRANSITION BETWEEN TIMER1 AND OSC1 (HS, XT, LP)
Q3
Q2
Q1
Q4
Q3
Q2
OSC1
Internal
SCS
(OSCCON<0>)
Program
PC + 2
PC
Note 1: Delay on internal system clock is eight oscillator cycles for synchronization.
Q1
T1OSI
Q4
Q1
PC + 4
Q1
TSCS
Clock
Counter
System
Q2
Q3
Q4
Q1
TDLY
TT1P
TOSC
2
1
3
4
5678
Q3
Q4
Q1
Q2
Q3
Q4
Q1
Q2
OSC1
Internal
SCS
(OSCCON<0>)
Program
PC
PC + 2
Note 1: TOST = 1024 TOSC (drawing not to scale).
T1OSI
System Clock
OSC2
TOST
Q1
PC + 6
TT1P
TOSC
TSCS
12
3
4
5
6
7
8
Counter
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