ATMEGA2561V ATMEL [ATMEL Corporation], ATMEGA2561V Datasheet - Page 62

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

Watchdog Timer
62
ATmega640/1280/1281/2560/2561
ATmega640/1280/1281/2560/2561 has an Enhanced Watchdog Timer (WDT). The
main features are:
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Figure 30. Watchdog Timer
The Watchdog Timer (WDT) is a timer counting cycles of a separate on-chip 128 kHz
oscillator. The WDT gives an interrupt or a system reset when the counter reaches a
given time-out value. In normal operation mode, it is required that the system uses the
WDR - Watchdog Timer Reset - instruction to restart the counter before the time-out
value is reached. If the system doesn't restart the counter, an interrupt or system reset
will be issued.
In Interrupt mode, the WDT gives an interrupt when the timer expires. This interrupt can
be used to wake the device from sleep-modes, and also as a general system timer. One
example is to limit the maximum time allowed for certain operations, giving an interrupt
when the operation has run longer than expected. In System Reset mode, the WDT
gives a reset when the timer expires. This is typically used to prevent system hang-up in
case of runaway code. The third mode, Interrupt and System Reset mode, combines the
other two modes by first giving an interrupt and then switch to System Reset mode. This
mode will for instance allow a safe shutdown by saving critical parameters before a sys-
tem reset.
The Watchdog always on (WDTON) fuse, if programmed, will force the Watchdog Timer
to System Reset mode. With the fuse programmed the System Reset mode bit (WDE)
and Interrupt mode bit (WDIE) are locked to 1 and 0 respectively. To further ensure pro-
gram security, alterations to the Watchdog set-up must follow timed sequences. The
sequence for clearing WDE and changing time-out configuration is as follows:
Clocked from separate On-chip Oscillator
3 Operating modes
Selectable Time-out period from 16ms to 8s
Possible Hardware fuse Watchdog always on (WDTON) for fail-safe mode
– Interrupt
– System Reset
– Interrupt and System Reset
WATCHDOG
RESET
OSCILLATOR
128kHz
WDIE
WDIF
WDE
WDP0
WDP1
WDP2
WDP3
MCU RESET
INTERRUPT
2549K–AVR–01/07