參數資料
型號: AT90S4433-8AC
廠商: Atmel
文件頁數: 65/126頁
文件大?。?/td> 0K
描述: IC MCU 4K FLSH 8MHZ A/D 32TQFP
標準包裝: 250
系列: AVR® 90S
核心處理器: AVR
芯體尺寸: 8-位
速度: 8MHz
連通性: SPI,UART/USART
外圍設備: 欠壓檢測/復位,POR,PWM,WDT
輸入/輸出數: 20
程序存儲器容量: 4KB(2K x 16)
程序存儲器類型: 閃存
EEPROM 大?。?/td> 256 x 8
RAM 容量: 128 x 8
電壓 - 電源 (Vcc/Vdd): 4 V ~ 6 V
數據轉換器: A/D 6x10b
振蕩器型: 外部
工作溫度: 0°C ~ 70°C
封裝/外殼: 32-TQFP
包裝: 托盤
43
AT90S/LS4433
1042H–AVR–04/03
Watchdog Timer
The Watchdog Timer is clocked from a separate On-chip Oscillator. By controlling the
Watchdog Timer prescaler, the Watchdog Reset interval can be adjusted as shown in
Table 6. See characterization data for typical values at other V
CC levels. The WDR
(Watchdog Reset) instruction resets the Watchdog Timer. Eight different clock cycle
periods can be selected to determine the reset period. If the reset period expires without
another Watchdog Reset, the AT90S4433 resets and executes from the Reset vector.
For timing details on the Watchdog Reset, refer to page 25.
To prevent unintentional disabling of the Watchdog, a special turn-off sequence must be
followed when the Watchdog is disabled. Refer to the description of the Watchdog Timer
Control Register for details.
Figure 35. Watchdog Timer
Watchdog Timer Control
Register – WDTCR
Bits 7..5 – Res: Reserved Bits
These bits are reserved bits in the AT90S4433 and will always read as zero.
Bit 4 – WDTOE: Watchdog Turn-off Enable
This bit must be set (one) when the WDE bit is cleared. Otherwise, the Watchdog will
not be disabled. Once set, hardware will clear this bit to zero after four clock cycles.
Refer to the description of the WDE bit for a Watchdog disable procedure.
Bit 3 – WDE: Watchdog Enable
When the WDE is set (one), the Watchdog Timer is enabled; if the WDE is cleared
(zero), the Watchdog Timer function is disabled. WDE can only be cleared if the
WDTOE bit is set (one). To disable an enabled Watchdog Timer, the following proce-
dure must be followed:
1.
In the same operation, write a logical “1” to WDTOE and WDE. A logical “1” must
be written to WDE even though it is set to one before the disable operation
starts.
2.
Within the next four clock cycles, write a logical “0” to WDE. This disables the
Watchdog.
Bit
765
4
321
0
$21 ($41)
WDTOE
WDE
WDP2
WDP1
WDP0
WDTCR
Read/Write
R
R/W
Initial Value
0
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