ATmega48PA datasheet(49/448 Pages) ATMEL

49 / 448 page

8161D–AVR–10/09

ATmega48PA/88PA/168PA/328P

Figure 10-5. Brown-out Reset During Operation

10.6

Watchdog System 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 t

TOUT. Refer to

page 50 for details on operation of the Watchdog Timer.

Figure 10-6. Watchdog System Reset During Operation

10.7

Internal Voltage Reference

ATmega48PA/88PA/168PA/328P 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.

10.7.1

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 318. To save power, the

reference is not always turned on. The reference is on during the following situations:

When the BOD is enabled (by programming the BODLEVEL [2:0] Fuses).

When the bandgap reference is connected to the Analog Comparator (by setting the

ACBG bit in ACSR).

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

VCC

RESET

TIME-OUT

INTERNAL

RESET

VBOT-

VBOT+

tTOUT

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