43
ATmega16M1/32M1/64M1 [DATASHEET]
8209E–AVR–11/2012
Figure 10-6. Watchdog reset during operation.
10.3
Internal voltage reference
Atmel ATmega16M1/32M1/64M1 features an internal bandgap reference. This reference is used for Brown-out
Detection, and it can be used as an input to the Analog Comparators or the ADC. The V
REF 2.56V reference to the
ADC, DAC or Analog Comparators is generated from the internal bandgap reference.
10.3.1
Voltage reference enable signals
and start-up time
The voltage reference has a start-up time that may influence the way it should be used. The start-up time is given
erence is on during the following situations:
1.
When the BOD is enabled (by programming the BODLEVEL [2..0] Fuse).
2.
When the bandgap reference is connected to the Analog Comparator (by setting the ACBG bit in ACSR).
3.
When the ADC is enabled.
4.
When the DAC is enabled.
Thus, when the BOD is not enabled, after setting the ACBG bit or enabling the ADC or the DAC, the user must
always allow the reference to start up before the output from the Analog Comparator or ADC or DAC is used. To
reduce power consumption in Power-down mode, the user can avoid the three conditions above to ensure that the
reference is turned off before entering Power-down mode.
10.4
Watchdog timer
10.4.1
Features
Clocked from separate on-chip oscillator
Three 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
10.4.2
Overview
The Atmel ATmega16M1/32M1/64M1 has an Enhanced Watchdog Timer (WDT). The WDT is a timer counting
cycles of a separate on-chip 128kHz 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.
CK
CC