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| 型号： | SST89E554A-40-C-NJ |
| 厂商： | SILICON STORAGE TECHNOLOGY INC |
| 元件分类： | 微控制器/微处理器 |
| 英文描述： | 8-BIT, FLASH, 40 MHz, MICROCONTROLLER, PQCC44 |
| 封装： | PLASTIC, MS-018AC, LCC-44 |
| 文件页数： | 43/87页 |
| 文件大小： | 996K |
| 代理商： | SST89E554A-40-C-NJ |
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48
Preliminary Specifications
FlashFlex51 MCU
SST89E554A / SST89V554A
2003 Silicon Storage Technology, Inc.
S71228-00-000
6/03
7.0 WATCHDOG TIMER
The device offers a programmable Watchdog Timer (WDT)
for fail safe protection against software deadlock and auto-
matic recovery.
To protect the system against software deadlock, the user
software must refresh the WDT within a user-defined time
period. If the software fails to do this periodical refresh, an
internal hardware reset will be initiated if enabled (WDRE=
1). The software can be designed such that the WDT times
out if the program does not work properly.
The WDT in the device uses the system clock (XTAL1) as
its time base. So strictly speaking, it is a watchdog counter
rather than a watchdog timer. The WDT register will incre-
ment every 344,064 crystal clocks. The upper 8-bits of the
time base register (WDTD) are used as the reload register
of the WDT.
The WDTS flag bit is set by WDT overflow and is not
changed by WDT reset. User software can clear WDTS by
writing “1” to it.
Figure 7-1 provides a block diagram of the WDT. Two SFRs
(WDTC and WDTD) control watchdog timer operation.
During idle mode, WDT operation is temporarily sus-
pended, and resumes upon an interrupt exit from idle.
The time-out period of the WDT is calculated as follows:
Period = (255 - WDTD) * 344064 * 1/fCLK (XTAL1)
where WDTD is the value loaded into the WDTD register
and fOSC is the oscillator frequency.
FIGURE
7-1: BLOCK DIAGRAM OF PROGRAMMABLE WATCHDOG TIMER
1228 F21.0
WDT Upper Byte
WDT Reset
Internal Reset
344064
clks
Counter
CLK (XTAL1)
Ext. RST
WDTC
WDTD
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相关代理商/技术参数 |
参数描述 |
|---|---|
| SST89E554RC | 制造商:SST 制造商全称:Silicon Storage Technology, Inc 功能描述:FlashFlex51 MCU |
| SST89E554RC-25-C-NI | 制造商:SST 制造商全称:Silicon Storage Technology, Inc 功能描述:FlashFlex51 MCU |
| SST89E554RC-25-C-NJ | 制造商:SST 制造商全称:Silicon Storage Technology, Inc 功能描述:FlashFlex51 MCU |
| SST89E554RC-25-C-PI | 制造商:SST 制造商全称:Silicon Storage Technology, Inc 功能描述:FlashFlex51 MCU |
| SST89E554RC-25-C-PJ | 制造商:SST 制造商全称:Silicon Storage Technology, Inc 功能描述:FlashFlex51 MCU |
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