ATMEGA2561V ATMEL [ATMEL Corporation], ATMEGA2561V Datasheet - Page 67

• Manufacturer Part Number: ATMEGA2561V
• Description: 8-bit Microcontroller with 64K/128K/256K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

2549K–AVR–01/07
Timer is in Interrupt Mode, and the corresponding interrupt is executed if time-out in the
Watchdog Timer occurs.
If WDE is set, the Watchdog Timer is in Interrupt and System Reset Mode. The first
time-out in the Watchdog Timer will set WDIF. Executing the corresponding interrupt
vector will clear WDIE and WDIF automatically by hardware (the Watchdog goes to Sys-
tem Reset Mode). This is useful for keeping the Watchdog Timer security while using
the interrupt. To stay in Interrupt and System Reset Mode, WDIE must be set after each
interrupt. This should however not be done within the interrupt service routine itself, as
this might compromise the safety-function of the Watchdog System Reset mode. If the
interrupt is not executed before the next time-out, a System Reset will be applied.
Table 30. Watchdog Timer Configuration
Note:
• Bit 4 - WDCE: Watchdog Change Enable
This bit is used in timed sequences for changing WDE and prescaler bits. To clear the
WDE bit, and/or change the prescaler bits, WDCE must be set.
Once written to one, hardware will clear WDCE after four clock cycles.
• Bit 3 - WDE: Watchdog System Reset Enable
WDE is overridden by WDRF in MCUSR. This means that WDE is always set when
WDRF is set. To clear WDE, WDRF must be cleared first. This feature ensures multiple
resets during conditions causing failure, and a safe start-up after the failure.
• Bit 5, 2:0 - WDP3:0: Watchdog Timer Prescaler 3, 2, 1 and 0
The WDP3:0 bits determine the Watchdog Timer prescaling when the Watchdog Timer
is running. The different prescaling values and their corresponding time-out periods are
shown in Table 31 on page 68.
WDTON
1
1
1
1
0
1. WDTON Fuse set to “0“ means programmed and “1” means unprogrammed.
(1)
WDE
0
0
1
1
x
ATmega640/1280/1281/2560/2561
WDIE
0
1
0
1
x
Mode
Stopped
Interrupt Mode
System Reset Mode
Interrupt and System
Reset Mode
System Reset Mode
Action on Time-out
None
Interrupt
Reset
Interrupt, then go to
System Reset Mode
Reset
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