ATmega88PA Automotive Atmel Corporation, ATmega88PA Automotive Datasheet - Page 47

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

11. System Control and Reset
11.1
11.2
9223B–AVR–09/11
Resetting the AVR
Reset Sources
During reset, all I/O Registers are set to their initial values, and the program starts execution
from the Reset Vector. For Atmel
must be a JMP – Absolute Jump – instruction to the reset handling routine. For the Atmel
ATmega48PA and Atmel ATmega88PA, the instruction placed at the Reset Vector must be an
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. This is also the case if the Reset Vector is in the Application sec-
t i o n w h i l e t h e I n t e r r u p t V e c t o r s a r e i n t h e B o o t s e c t i o n o r v i c e v e r s a ( A t m e l
ATmega88PA/168PA only). The circuit diagram in
logic.
The I/O ports of the AVR are immediately reset to their initial state when a reset 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
27.
The Atmel
• 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 System Reset. The MCU is reset when the Watchdog Timer period expires and
• Brown-out Reset. The MCU is reset when the supply voltage V
threshold (V
than the minimum pulse length.
the Watchdog System Reset mode is enabled.
Reset threshold (V
Atmel ATmega48PA/88PA/168PA [Preliminary]
Table 29-5 on page 318
®
ATmega48PA/88PA/168PA has four sources of reset:
POT
).
BOT
) and the Brown-out Detector is enabled.
defines the electrical parameters of the reset circuitry.
®
ATmega168PA the instruction placed at the Reset Vector
Figure 11-1 on page 48
CC
is below the Brown-out
“Clock Sources” on page
shows the reset
47