ATTINY48_1 Datasheet, PDF (41/266 Pages) ATMEL Corporation – 8-bit Microcontroller with 4/8K Bytes In-System Programmable Flash

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
CC
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+ =
V_BOT + V_HYST/2 and V_BOT- = V_BOT - V_HYST/2. When the BOD is enabled, and V_CC 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 (V_BOT+ 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
V_CC
V_BOT-
V_BOT+
RESET
TIME-OUT
t_TOUT
INTERNAL
RESET
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