Datasheet

38
2586D–AVR–02/06
ATtiny25/45/85
Figure 9-3. MCU Start-up, RESET Extended Externally
9.0.4 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 Table 9-1) will generate a reset, even if the clock is not run-
ning. 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 9-4. External Reset During Operation
9.0.5 Brown-out Detection
ATtiny25/45/85 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+
=
V
BOT
+ V
HYST
/2 and V
BOT-
= V
BOT
- V
HYST
/2.
RESET
TIME-OUT
I
NTERNAL
RESET
t
TOUT
V
POT
V
RST
V
CC
CC
Table 9-2. BODLEVEL Fuse Coding
(1)
BODLEVEL [2:0] Fuses Min V
BOT
Typ V
BOT
Max V
BOT
Units
111 BOD Disabled