参数资料
型号: PIC12F683T-E/MF
厂商: Microchip Technology
文件页数: 102/176页
文件大小: 0K
描述: IC MCU FLASH 2KX14 8DFN
Digi-Key 应用说明: AN0005 PWM Example with Microchip's CCP Module
AN0005 Example Code
标准包装: 3,300
系列: PIC® 12F
核心处理器: PIC
芯体尺寸: 8-位
速度: 20MHz
外围设备: 欠压检测/复位,POR,PWM,WDT
输入/输出数: 5
程序存储器容量: 3.5KB(2K x 14)
程序存储器类型: 闪存
EEPROM 大小: 256 x 8
RAM 容量: 128 x 8
电压 - 电源 (Vcc/Vdd): 2 V ~ 5.5 V
数据转换器: A/D 4x10b
振荡器型: 内部
工作温度: -40°C ~ 125°C
封装/外壳: 8-VDFN 裸露焊盘
包装: 带卷 (TR)
配用: AC164324-ND - MODULE SKT FOR MPLAB 8DFN/16QFN
XLT08DFN2-ND - SOCKET TRANSITION ICE 14DIP/8DFN
AC162058-ND - HEADER MPLAB ICD2 FOR PIC12F683
I3-DB12F683-ND - BOARD DAUGHTER ICEPIC3
XLT08DFN-ND - SOCKET TRANSITION ICE 8DFN
AC164032-ND - ADAPTER PICSTART PLUS 8DFN/DIP
AC124001-ND - MODULE SKT PROMATEII 8DIP/SOIC
2007 Microchip Technology Inc.
DS41211D-page 29
PIC12F683
3.8
Fail-Safe Clock Monitor
The Fail-Safe Clock Monitor (FSCM) allows the device
to continue operating should the external oscillator fail.
The FSCM can detect oscillator failure any time after
the Oscillator Start-up Timer (OST) has expired. The
FSCM is enabled by setting the FCMEN bit in the
Configuration Word register (CONFIG). The FSCM is
applicable to all external oscillator modes (LP, XT, HS,
EC, RC and RCIO).
FIGURE 3-8:
FSCM BLOCK DIAGRAM
3.8.1
FAIL-SAFE DETECTION
The FSCM module detects a failed oscillator by
comparing the external oscillator to the FSCM sample
clock. The sample clock is generated by dividing the
LFINTOSC by 64. See Figure 3-8. Inside the fail
detector block is a latch. The external clock sets the
latch on each falling edge of the external clock. The
sample clock clears the latch on each rising edge of the
sample clock. A failure is detected when an entire
half-cycle of the sample clock elapses before the
primary clock goes low.
3.8.2
FAIL-SAFE OPERATION
When the external clock fails, the FSCM switches the
device clock to an internal clock source and sets the bit
flag OSFIF of the PIR1 register. Setting this flag will
generate an interrupt if the OSFIE bit of the PIE1
register is also set. The device firmware can then take
steps to mitigate the problems that may arise from a
failed clock. The system clock will continue to be
sourced from the internal clock source until the device
firmware successfully restarts the external oscillator
and switches back to external operation.
The internal clock source chosen by the FSCM is
determined by the IRCF<2:0> bits of the OSCCON
register. This allows the internal oscillator to be
configured before a failure occurs.
3.8.3
FAIL-SAFE CONDITION CLEARING
The Fail-Safe condition is cleared after a Reset,
executing a SLEEP instruction or toggling the SCS bit
of the OSCCON register. When the SCS bit is toggled,
the OST is restarted. While the OST is running, the
device continues to operate from the INTOSC selected
in OSCCON. When the OST times out, the Fail-Safe
condition is cleared and the device will be operating
from the external clock source. The Fail-Safe condition
must be cleared before the OSFIF flag can be cleared.
3.8.4
RESET OR WAKE-UP FROM SLEEP
The FSCM is designed to detect an oscillator failure
after the Oscillator Start-up Timer (OST) has expired.
The OST is used after waking up from Sleep and after
any type of Reset. The OST is not used with the EC or
RC Clock modes so that the FSCM will be active as
soon as the Reset or wake-up has completed. When
the FSCM is enabled, the Two-Speed Start-up is also
enabled. Therefore, the device will always be executing
code while the OST is operating.
External
LFINTOSC
÷ 64
S
R
Q
31 kHz
(~32
μs)
488 Hz
(~2 ms)
Clock Monitor
Latch
Clock
Failure
Detected
Oscillator
Clock
Q
Sample Clock
Note:
Due to the wide range of oscillator start-up
times, the Fail-Safe circuit is not active
during oscillator start-up (i.e., after exiting
Reset or Sleep). After an appropriate
amount of time, the user should check the
OSTS bit of the OSCCON register to verify
the oscillator start-up and that the system
clock
switchover
has
successfully
completed.
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