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ATMEGA8515-16PI(2010) View Datasheet(PDF) - Atmel Corporation

Part Name
Description
View to exact match
ATMEGA8515-16PI
(Rev.:2010)
Atmel
Atmel Corporation Atmel
ATMEGA8515-16PI Datasheet PDF : 257 Pages
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ATmega8515(L)
System Control and
Reset
Resetting the AVR
Reset Sources
During Reset, all I/O Registers are set to their initial values, and the program starts exe-
cution from the Reset Vector. The instruction placed at the Reset Vector must be a
RJMP 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 section
while the Interrupt Vectors are in the Boot section or vice versa. The circuit diagram in
Figure 22 shows the reset logic. Table 18 defines the electrical parameters of the reset
circuitry.
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
CKSEL Fuses. The different selections for the delay period are presented in “Clock
Sources” on page 35.
The ATmega8515 has four sources of reset:
• Power-on Reset. The MCU is reset when the supply voltage is below the Power-on
Reset threshold (VPOT).
• External Reset. The MCU is reset when a low level is present on the RESET pin for
longer than the minimum pulse length.
• 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 VCC is below the
Brown-out Reset threshold (VBOT) and the Brown-out Detector is enabled.
45
2512K–AVR–01/10
 

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