參數(shù)資料
型號: MR83C154XXX-25/883D
廠商: ATMEL CORP
元件分類: 微控制器/微處理器
英文描述: 8-BIT, MROM, 25 MHz, MICROCONTROLLER, CQCC44
封裝: LCC-44
文件頁數(shù): 115/141頁
文件大?。?/td> 7628K
代理商: MR83C154XXX-25/883D
45
2486AA–AVR–02/2013
ATmega8(L)
Timed Sequences
for Changing the
Configuration of
the Watchdog
Timer
The sequence for changing the Watchdog Timer configuration differs slightly between the safety
levels. Separate procedures are described for each level.
Safety Level 1
(WDTON Fuse
Unprogrammed)
In this mode, the Watchdog Timer is initially disabled, but can be enabled by writing the WDE bit
to 1 without any restriction. A timed sequence is needed when changing the Watchdog Time-out
period or disabling an enabled Watchdog Timer. To disable an enabled Watchdog Timer and/or
changing the Watchdog Time-out, the following procedure must be followed:
1.
In the same operation, write a logic one to WDCE and WDE. A logic one must be written
to WDE regardless of the previous value of the WDE bit
2.
Within the next four clock cycles, in the same operation, write the WDE and WDP bits as
desired, but with the WDCE bit cleared
Safety Level 2
(WDTON Fuse
Programmed)
In this mode, the Watchdog Timer is always enabled, and the WDE bit will always read as one. A
timed sequence is needed when changing the Watchdog Time-out period. To change the
Watchdog Time-out, the following procedure must be followed:
1.
In the same operation, write a logical one to WDCE and WDE. Even though the WDE
always is set, the WDE must be written to one to start the timed sequence
Within the next four clock cycles, in the same operation, write the WDP bits as desired, but with
the WDCE bit cleared. The value written to the WDE bit is irrelevant.
Assembly Code Example
WDT_off:
; reset WDT
WDR
; Write logical one to WDCE and WDE
in
r16, WDTCR
ori
r16, (1<<WDCE)|(1<<WDE)
out
WDTCR, r16
; Turn off WDT
ldi
r16, (0<<WDE)
out
WDTCR, r16
ret
C Code Example
void
WDT_off(void)
{
/* reset WDT */
_WDR();
/* Write logical one to WDCE and WDE */
WDTCR |= (1<<WDCE) | (1<<WDE);
/* Turn off WDT */
WDTCR = 0x00;
}
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