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參數(shù)資料
| 型號(hào)： | W79E225A |
| 廠商： | WINBOND ELECTRONICS CORP |
| 元件分類： | 8位微控制器 |
| 英文描述： | 8-BIT MICROCONTROLLER |
| 中文描述： | 8位微控制器 |
| 文件頁(yè)數(shù)： | 102/200頁(yè) |
| 文件大小： | 3644K |
| 代理商： | W79E225A |
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Preliminary W79E225A/227A Data Sheet
Publication Release Date: December 14, 2007
- 102 -
Revision A2.0
13. WATCHDOG TIMER
The Watchdog Timer is a free-running timer that can be programmed to serve as a system monitor, a
time-base generator or an event timer. It is basically a set of dividers that divide the system clock to
determine the time-out interval. When the time-out occurs, a flag is set, which can generate an
interrupt or a system reset, if enabled. The interrupt will occur if its interrupt and global interrupt
enables are set. The interrupt and reset functions are independent of each other and may be used
separately or together.
The main use of the Watchdog Timer is as a system monitor. In case of power glitches or
electromagnetic interference, the processor may begin to execute errant code. The Watchdog Timer
helps W79E225/227 recovers from these states. During development, the code is first written without
the watchdog interrupt or reset. Then, the watchdog interrupt is enabled to identify code locations
where the interrupt occurs, and instructions are inserted to reset the Watchdog Timer in these
locations. In the final version, the watchdog interrupt is disabled, and the watchdog reset is enabled. If
errant code is executed, the Watchdog Timer is not reset at the required times, so a Watchdog Timer
reset occurs.
When used as a simple timer, the reset and interrupt functions are disabled. The Watchdog Timer can
be started by RWT and sets the WDIF flag after the selected time interval. Meanwhile, the program
polls the WDIF flag to find out when the selected time interval has passed. Alternatively, the Watchdog
Timer can also be used as a very long timer. In this case, the interrupt feature is enabled.
Figure 13-1: Watchdog Timer
The Watchdog Timer should be started by RWT because this ensures that the timer starts from a
known state. The RWT bit is self-clearing; i.e., after writing a 1 to this bit, the bit is automatically
cleared. After setting RWT, the Watchdog Timer begins counting clock cycles. The time-out interval is
selected by WD1 and WD0 (CKCON.7 and CKCON.6).
WD1
WD0
INTERRUPT
TIME-OUT
RESET
TIME-OUT
2
17
+ 512
2
20
+ 512
2
23
+ 512
2
26
+ 512
NUMBER OF
CLOCKS
TIME
@ 10 MHZ
TIME
@ 11.0592 MHZ
TIME
@ 25 MHZ
0
0
2
17
2
20
2
23
2
26
131072
13.11 mS
11.85 mS
5.24 mS
0
1
1048576
104.86 mS
94.81 mS
41.94 mS
1
0
8388608
838.86 mS
758.52 mS
335.54 mS
1
1
67108864
6710.89 mS
6068.15 mS
2684.35 mS
Table 13-1: Time-out values for the Watchdog Timer
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| W79E225AFG | 8-BIT MICROCONTROLLER |
| W79E225APG | 8-BIT MICROCONTROLLER |
| W79E227A | 8-BIT MICROCONTROLLER |
| W79E227AFG | 8-BIT MICROCONTROLLER |
| W79E227APG | 8-BIT MICROCONTROLLER |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| W79E225A_08 | 制造商:WINBOND 制造商全稱:Winbond 功能描述:8-bit Microcontroller |
| W79E225A_226A_227A | 制造商:WINBOND 制造商全稱:Winbond 功能描述:W79E225A_226A_227A_A7_SC5（中文） |
| W79E225AFG | 制造商:WINBOND 制造商全稱:Winbond 功能描述:8-bit Microcontroller |
| W79E225ALG | 制造商:Nuvoton Technology Corp 功能描述:IC MCU 16K EPROM FLASH 48LQFP |
| W79E225APG | 制造商:Nuvoton Technology Corp 功能描述:IC MCU 16K EPROM FLASH 44PLCC |
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