ATtiny88 datasheet(41/266 Pages) ATMEL

41 / 266 page

8008C–AVR–03/09

ATtiny48/88

8.2.2

External Reset

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

minimum pulse width (see Table 21-3 on page 204) will generate 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. The External Reset can be disabled by the

RSTDISBL fuse, see Table 20-4 on page 185.

Figure 8-4.

External Reset During Operation

8.2.3

Brown-out Detection

ATtiny48/88 has an On-chip Brown-out Detection (BOD) circuit for monitoring the V

CC level dur-

ing 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 VCC decreases to a

value below the trigger level (V

BOT- in Figure 8-5), the Brown-out Reset is immediately activated.

When V

CC increases above the trigger level (VBOT+ in Figure 8-5), 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 Characterizations” on page 204.

Figure 8-5.

Brown-out Reset During Operation

VCC

RESET

TIME-OUT

INTERNAL

RESET

VBOT-

VBOT+

tTOUT

ATtiny88 Datasheet(PDF) 41 Page - ATMEL Corporation

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