Rainbow Electronics ATtiny43U - Manual (Page 50)

50
8048B–AVR–03/09
ATtiny43U
9.4 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 20-4 on page 158 ) 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 9-4. External Reset During Operation
9.5 Brown-out Detection
ATtiny43U 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.
When the BOD is enabled, and V
CC
decreases to a value below the trigger level (V
BOT-
in Figure
9-5 on page 50 ), the Brown-out Reset is immediately activated. When V
CC
increases above the
trigger level (V
BOT+
in Figure 9-5 on page 50 ), 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 Table 20-4 on page 158 .
Figure 9-5. Brown-out Reset During Operation
CC
V
CC
RESET
TIME-OUT
INTERNAL
RESET
V
BOT-
V
BOT+
t
TOUT