ATtiny44 datasheet(41/236 Pages) ATMEL

41 / 236 page

8006H–AVR–10/09

ATtiny24/44/84

8.2.2

External Reset

An External Reset is generated by a low level on the RESET pin if enabled. Reset pulses longer

than the minimum pulse width (see “System and Reset Characteristics” on page 177) will gener-

ate a reset, even if the clock is not running. Shorter pulses are not guaranteed to generate a

reset. When the applied signal reaches the Reset Threshold Voltage – V

RST – on its positive

edge, the delay counter starts the MCU after the Time-out period – t

TOUT – has expired.

Figure 8-4.

External Reset During Operation

8.2.3

Brown-out Detection

ATtiny24/44/84 has an On-chip Brown-out Detection (BOD) circuit for monitoring the V

CC 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

8-5 on page 41), the Brown-out Reset is immediately activated. When V

CC increases above the

trigger level (V

BOT+ in Figure 8-5 on page 41), the delay counter starts the MCU after the Time-

out period t

TOUT 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 177.

Figure 8-5.

Brown-out Reset During Operation

VCC

RESET

TIME-OUT

INTERNAL

RESET

VBOT-

VBOT+

tTOUT

ATtiny44 Datasheet(PDF) 41 Page - ATMEL Corporation

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