ATmega88PA Automotive Atmel Corporation, ATmega88PA Automotive Datasheet - Page 40

• Manufacturer Part Number: ATmega88PA Automotive
• Manufacturer: Atmel Corporation

9. System Control and Reset
9.1
9.2
40
Resetting the AVR
Reset Sources
Atmel ATtiny24/44/84 [Preliminary]
During reset, all I/O Registers are set to their initial values, and the program starts execution
from the Reset Vector. The instruction placed at the Reset Vector must be a RJMP – Relative
Jump – instruction to the reset handling routine. If the program never enables an interrupt
source, the Interrupt Vectors are not used, and regular program code can be placed at these
locations. The circuit diagram in
page 42
The I/O ports of the Atmel
source goes active. This does not require any clock source to be running.
After all reset sources have gone inactive, a delay counter is invoked, stretching the internal
reset. This allows the power to reach a stable level before normal operation starts. The
time-out period of the delay counter is defined by the user through the SUT and CKSEL
Fuses. The different selections for the delay period are presented in
26.
The Atmel 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
• External Reset. The MCU is reset when a low level is present on the RESET pin for longer
• Watchdog Reset. The MCU is reset when the watchdog timer period expires and the
• Brown-out Reset. The MCU is reset when the supply voltage V
threshold (V
than the minimum pulse length when RESET function is enabled.
watchdog is enabled.
reset threshold (V
defines the electrical parameters of the reset circuitry.
POT
).
BOT
) and the brown-out detector is enabled.
®
AVR
Figure 9-1 on page 41
®
are immediately reset to their initial state when a reset
shows the reset logic.
CC
“Clock Sources” on page
is below the brown-out
7701E–AVR–02/11
Table 9-1 on