ATTINY84_14 Datasheet, PDF (40/238 Pages) ATMEL Corporation – Non-Volatile Program and Data Memories

8.2 Reset Sources
The ATtiny24/44/84 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.
8.2.1
Power-on Reset
A Power-on Reset (POR) pulse is generated by an On-chip detection circuit. The detection level
is defined in “System and Reset Characteristics” on page 177. 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 8-2. MCU Start-up, RESET Tied to V_CC
V_CC
V_POT
RESET
V_RST
TIME-OUT
t_TOUT
INTERNAL
RESET
Figure 8-3. MCU Start-up, RESET Extended Externally
V_CC
V_POT
RESET
V_RST
TIME-OUT
t_TOUT
INTERNAL
RESET
40 ATtiny24/44/84
8006K–AVR–10/10