45
AT90PWM216/316 [DATASHEET]
7710H–AVR–07/2013
8.8.2
Voltage Reference Characteristics
Note:
1. Values are guidelines only.
8.9
Watchdog Timer
AT90PWM216/316 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 8-7.
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
Table 8-4.
Internal Voltage Reference Characteristics
Symbol
Parameter
Condition
Min.
Typ.
Max.
Units
VBG
Bandgap reference voltage
1.1
V
tBG
Bandgap reference start-up time
40
s
IBG
Bandgap reference current consumption
15
A
128 KHz
OSCILLATOR
MCU RESET
INTERRUPT
WDIE
WDIF
OSC/2K
OSC/4K
OSC/
8
K
WDP3