ATtiny261-ESMZ datasheet(43/227 Pages) ATMEL

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7753C–AVR–07/09

ATtiny261/ATtiny461/ATtiny861

9.0.5

Brown-out Detection

ATtiny261/461/861 has an On-chip Brown-out Detection (BOD) circuit for monitoring the V

level during operation by comparing it to a fixed trigger level. The trigger level for the BOD can

be selected by the BODLEVEL Fuses. The trigger level has a hysteresis to ensure spike free

Brown-out Detection. The hysteresis on the detection level should be interpreted as V

BOT+ =

BOT + VHYST/2 and VBOT- = VBOT - VHYST/2.

When the BOD is enabled, and V

CC decreases to a value below the trigger level (VBOT- in Figure

9-5), the Brown-out Reset is immediately activated. When V

CC increases above the trigger level

BOT+ in Figure 9-5), the delay counter starts the MCU after the Time-out period tTOUT has

expired.

The BOD circuit will only detect a drop in V

CC if the voltage stays below the trigger level for lon-

ger than t

BOD given in “System and Reset Characteristics” on page 190.

Figure 9-5.

Brown-out Reset During Operation

9.0.6

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 t

TOUT. Refer to

page 44 for details on operation of the Watchdog Timer.

Figure 9-6.

Watchdog Reset During Operation

VCC

RESET

TIME-OUT

INTERNAL

RESET

VBOT-

VBOT+

tTOUT

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