Rainbow Electronics ATtiny43U - Manual (Page 49)

49
8048B–AVR–03/09
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.
9.3 Power-on Reset
A Power-on Reset (POR) pulse is generated by an On-chip detection circuit. The detection level
is defined in
Table 20-4 on page 158 . The POR is activated whenever V
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
V
CC