ATMEGA640 datasheet(60/436 Pages) MICROCHIP

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ATmega640/V-1280/V-1281/V-2560/V-2561/V [DATASHEET]

DS40002211A

Figure 12-5. Brown-out Reset During Operation

12.2.4

Watchdog Reset

When the Watchdog times out, it will generate a short reset pulse of one CK cycle duration. On the falling edge of

this pulse, the delay timer starts counting the Time-out period tTOUT. See “Watchdog Timer” on page 53. for details

on operation of the Watchdog Timer.

Figure 12-6. Watchdog Reset During Operation

12.3 Internal Voltage Reference

ATmega640/1280/1281/2560/2561 features an internal bandgap reference. This reference is used for Brown-out

Detection, and it can be used as an input to the Analog Comparator or the ADC.

12.3.1

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

in “System and Reset Characteristics” on page 360. To save power, the reference is not always turned on. The ref-

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.

Thus, when the BOD is not enabled, after setting the ACBG bit or enabling the ADC, the user must always allow

the reference to start up before the output from the Analog Comparator or ADC is used. To reduce power con-

sumption 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.

AVCC

RESET

TIME-OUT

INTERNAL

RESET

VBOT-

VBOT+

tTOUT

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