Datasheet

33
ATtiny13
2535E–AVR–10/04
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 12) 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.
Figure 16. External Reset During Operation
Brown-out Detection ATtiny13 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 inter-
preted as V
BOT+
= V
BOT
+ V
HYST
/2 and V
BOT-
= V
BOT
- V
HYST
/2.
Note: 1. V
BOT
may be below nominal minimum operating voltage for some devices. For
devices where this is the case, the device is tested down to V
CC
= V
BOT
during the
production test. This guarantees that a Brown-out Reset will occur before V
CC
drops
to a voltage where correct operation of the microcontroller is no longer guaranteed.
When the BOD is enabled, and V
CC
decreases to a value below the trigger level (V
BOT-
in Figure 17), the Brown-out Reset is immediately activated. When V
CC
increases above
the trigger level (V
BOT+
in Figure 17), 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 longer than t
BOD
given in Table 14.
CC
Table 13. BODLEVEL Fuse Coding
(1)
BODLEVEL [1..0] Fuses Min V
BOT
Typ V
BOT
Max V
BOT
Units
11 BOD Disabled
10 1.8
V01 2.7
00 4.3
Table 14. Brown-out Characteristics
Symbol Parameter Min Typ Max Units
V
HYST
Brown-out Detector Hysteresis 50 mV
t
BOD
Min Pulse Width on Brown-out Reset 2 µs