ATMEGA406 datasheet(46/263 Pages) ATMEL

46 / 263 page

2548E–AVR–07/06

ATmega406

9.4

9.4.1

MCUSR – MCU Status Register

The MCU Status Register provides information on which reset source caused an MCU reset.

• Bits 7:5 – Res: Reserved Bits

These bits are reserved bits in the ATmega406, and will always read as zero.

• Bit 4 – JTRF: JTAG Reset Flag

This bit is set if a reset is being caused by a logic one in the JTAG Reset Register selected by

the JTAG instruction AVR_RESET. This bit is reset by a Power-on Reset, or by writing a logic

zero to the flag.

• Bit 3 – WDRF: Watchdog Reset Flag

This bit is set if a Watchdog Reset occurs. The bit is reset by a Power-on Reset, or by writing a

logic zero to the flag.

• Bit 2 – BODRF: Brown-out Reset Flag

This bit is set if a Brown-out Reset occurs. The bit is reset by a Power-on Reset, or by writing a

logic zero to the flag.

• Bit 1 – EXTRF: External Reset Flag

This bit is set if an External Reset occurs. The bit is reset by a Power-on Reset, or by writing a

logic zero to the flag.

• Bit 0 – PORF: Power-on Reset Flag

This bit is set if a Power-on Reset occurs. The bit is reset only by writing a logic zero to the flag.

To make use of the Reset flags to identify a reset condition, the user should read and then reset

the MCUSR as early as possible in the program. If the register is cleared before another reset

occurs, the source of the reset can be found by examining the reset flags.

Bit

76543210

0x34 (0x54)

–

JTRF

WDRF

BODRF

EXTRF

PORF

MCUSR

Read/Write

R/W

Initial Value

See Bit Description

ATMEGA406 Datasheet(PDF) 46 Page - ATMEL Corporation