AT90PWM2(2005) View Datasheet(PDF) - Atmel Corporation

Part Name

Description

Manufacturer

AT90PWM2
(Rev.:2005)

8-bit Microcontroller with 8K Bytes In-System Programmable Flash

Atmel Corporation 

Watchdog Timer

AT90PWM2/3 has an Enhanced Watchdog Timer (WDT). The main features are:

• Clocked from separate On-chip Oscillator

• 3 Operating modes

– Interrupt

– System Reset

– Interrupt and System Reset

• Selectable Time-out period from 16ms to 8s

• Possible Hardware fuse Watchdog always on (WDTON) for fail-safe mode

Figure 23. Watchdog Timer

128 KHz

OSCILLATOR

WDP3

MCU RESET

WDIF

WDIE

INTERRUPT

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 Timer Always On” (WDTON) fuse, if programmed, will force the Watch-

dog 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 program security, alterations to the Watchdog set-up must follow timed

sequences. The sequence for clearing WDE and changing time-out configuration is as

follows:

50 AT90PWM2/3

4317B–AVR–02/05

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