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參數資料
| 型號： | W77E468 |
| 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 |
| 文件頁數： | 63/84頁 |
| 文件大小： | 531K |
| 代理商： | W77E468 |
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Preliminary W77E468
Publication Release Date: January 1999
- 63 - Revision A1
The main use of the Watchdog timer is as a system monitor. This is important in real-time control
applications. In case of some power glitches or electro-magnetic interference, the processor may
begin to execute errant code. If this is left unchecked the entire system may crash. Using the
watchdog timer interrupt during software development will allow the user to select ideal watchdog
reset locations. The code is first written without the watchdog interrupt or reset. Then the watchdog
interrupt is enabled to identify code locations where interrupt occurs. The user can now insert
instructions to reset the watchdog timer which will allow the code to run without any watchdog timer
interrupts. Now the watchdog timer reset is enabled and the watchdog interrupt may be disabled,. If
any errant code is executed now, then the reset watchdog timer instructions will not be executed at
the required instants and watchdog reset will occur.
The watchdog time-out selection will result in different time-out values depending on the clock speed.
The reset, when enabled, will occur 512 clocks after the time-out has occurred.
Table 9. Time-out values for the Watchdog timer
WD1
WD0
Watchdog
Interval
2
17
2
20
2
23
2
26
Number of
Clocks
Time
@1.8432 MHz
Time
@10 MHz
Time
@25 MHz
0
0
131072
71.11 mS
13.11 mS
5.24 mS
0
1
1048576
568.89 mS
104.86 mS
41.94 mS
1
0
8388608
4551.11 mS
838.86 mS
335.54 mS
1
1
67108864
36408.88 mS
6710.89 mS
2684.35 mS
The Watchdog timer will de disabled by a power-on/fail reset. The Watchdog timer reset does not
disable the watchdog timer, but will restart it. In general, software should restart the timer to put it into
a known state.
The control bits that support the Watchdog timer are discussed below.
WATCHDOG CONTROL
WDIF: WDCON.3 - Watchdog Timer Interrupt flag. This bit is set whenever the time-out occurs in
the watchdog timer. If the Watchdog interrupt is enabled (EIE.4), then an interrupt will occur
(if the global interrupt enable is set and other interrupt requirements are met). Software or any
reset can clear this bit.
WTRF: WDCON.2 - Watchdog Timer Reset flag. This bit is set whenever a watchdog reset occurs.
This bit is useful for determined the cause of a reset. Software must read it, and clear it
manually. A Power-fail reset will clear this bit. If EWT = 0, then this bit will not be affected by
the watchdog timer.
EWT:
WDCON.1 - Enable Watchdog timer Reset. This bit when set to 1 will enable the Watchdog
timer reset function. Setting this bit to 0 will disable the Watchdog timer reset function, but
will leave the timer running
RWT:
WDCON.0 - Reset Watchdog Timer. This bit is used to clear the Watchdog timer and to
restart it. This bit is self-clearing, so after the software writes 1 to it the hardware will
automatically clear it. If the Watchdog timer reset is enabled, then the RWT has to be set by
the user within 512 clocks of the time-out. If this is not done then a Watchdog timer reset will
occur.
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相關代理商/技術參數 |
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| W77E468F-25 | 制造商:WINBOND 制造商全稱:Winbond 功能描述:8 BIT MICROCONTROLLER |
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| W77E516 | 制造商:WINBOND 制造商全稱:Winbond 功能描述:8-BIT MICROCONTROLLER |
| W77E516-25 | 制造商:WINBOND 制造商全稱:Winbond 功能描述:8-BIT MICROCONTROLLER |
| W77E516-40 | 制造商:WINBOND 制造商全稱:Winbond 功能描述:8-BIT MICROCONTROLLER |
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