ATXMEGA256A3B_09 ATMEL [ATMEL Corporation], ATXMEGA256A3B_09 Datasheet - Page 23

• Manufacturer Part Number: ATXMEGA256A3B_09
• Description: 8/16-bit XMEGA A3B Microcontroller
• Manufacturer: ATMEL [ATMEL Corporation]

12. System Control and Reset
12.1
12.2
12.3
12.3.1
12.3.2
12.3.3
12.3.4
8116F–AVR–09/09
Features
Resetting the AVR
Reset Sources
Power-On Reset
External Reset
Watchdog Reset
Brown-Out Reset
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During reset, all I/O registers are set to their initial values. The SRAM content is not reset. Appli-
cation execution starts from the Reset Vector. The instruction placed at the Reset Vector should
be an Absolute Jump (JMP) instruction to the reset handling routine. By default the Reset Vector
address is the lowest Flash program memory address, ‘0’, but it is possible to move the Reset
Vector to the first address in the Boot Section.
The I/O ports of the AVR are immediately tri-stated when a reset source goes active.
The reset functionality is asynchronous, so no running clock is required to reset the device.
After the device is reset, the reset source can be determined by the application by reading the
Reset Status Register.
The MCU is reset when the supply voltage VCC is below the Power-on Reset threshold voltage.
The MCU is reset when a low level is present on the RESET pin.
The MCU is reset when the Watchdog Timer period expires and the Watchdog Reset is enabled.
The Watchdog Timer runs from a dedicated oscillator independent of the System Clock. For
more details see
The MCU is reset when the supply voltage VCC is below the Brown-Out Reset threshold voltage
and the Brown-out Detector is enabled. The Brown-out threshold voltage is programmable.
Multiple reset sources for safe operation and device reset
Asynchronous reset
Reset status register
– Power-On Reset
– External Reset
– Watchdog Reset
– Brown-Out Reset
– JTAG Reset
– PDI reset
– Software reset
– No running clock in the device is required for reset
The Watchdog Timer runs from separate, dedicated oscillator
Accurate, programmable Brown-Out levels
”WDT - Watchdog Timer” on page
24.
XMEGA A3B
23