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50
8048C–AVR–02/12
ATtiny43U
9.2
Reset Sources
The ATtiny43U has four sources of reset:
Power-on Reset. The MCU is reset when the supply voltage is below the Power-on Reset
threshold (V
POT).
External Reset. The MCU is reset when a low level is present on the RESET pin for longer
than the minimum pulse length when RESET function is enabled.
Watchdog Reset. The MCU is reset when the Watchdog Timer period expires and the
Watchdog is enabled.
Brown-out Reset. The MCU is reset when the supply voltage V
CC is below the Brown-out
Reset threshold (V
BOT) and the Brown-out Detector is enabled.
9.2.1
Power-on Reset
A Power-on Reset (POR) pulse is generated by an On-chip detection circuit. The detection level
CC is below the detection
level. The POR circuit can be used to trigger the Start-up Reset, as well as to detect a failure in
supply voltage.
A Power-on Reset (POR) circuit ensures that the device is reset from Power-on. Reaching the
Power-on Reset threshold voltage invokes the delay counter, which determines how long the
device is kept in RESET after V
CC rise. The RESET signal is activated again, without any delay,
when V
CC decreases below the detection level.
Figure 9-2.
MCU Start-up, RESET Tied to V
CC
Figure 9-3.
MCU Start-up, RESET Extended Externally
V
RESET
TIME-OUT
INTERNAL
RESET
t
TOUT
V
POT
V
RST
CC
RESET
TIME-OUT
INTERNAL
RESET
t
TOUT
V
POT
V
RST
VCC