ATA8742 ATMEL Corporation, ATA8742 Datasheet - Page 55

• Manufacturer Part Number: ATA8742
• Manufacturer: ATMEL Corporation

16. System Control and Reset
16.0.1
16.0.2
9151A–INDCO–07/09
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. 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 57
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 dif-
ferent selections for the delay period are presented in
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
• External Reset. The MCU is reset when a low level is present on the RESET pin for longer than
• 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
the minimum pulse length when RESET function is enabled.
Watchdog is enabled.
threshold (V
defines the electrical parameters of the reset circuitry.
POT
BOT
).
) and the Brown-out Detector is enabled.
Figure 16-1 on page 56
“Clock Sources” on page
shows the reset logic.
CC
is below the Brown-out Reset
ATA8742
42.
Table 16-1 on
55