MCU Status Register

When using the I/O specific commands IN and OUT, the I/O addresses 0x00 - 0x3F must be used. When addressing I/O Registers as data space using LD and ST instructions, 0x20 must be added to these offset addresses.

Name:
MCUSR
Offset:
0x54 [ID-000004d0]
Reset:
0x0X
Access:
When addressing as I/O Register: address offset is 0x34
Bit76543210
WDRTBORFEXTRFPORF
AccessR/WR/WR/WR/W
Resetxxx0

Bit 3 – WDRT: Watchdog System Reset Flag

Watchdog System Reset Flag

This bit is set if a Watchdog System Reset occurs. The bit is reset by a Power-on Reset, or by writing a '0' to the flag.

Bit 2 – BORF: Brown-out Reset Flag

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 '0' to the flag.

Bit 1 – EXTRF: External Reset Flag

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 '0' to the flag.

Bit 0 – PORF: Power-on Reset Flag

Power-on Reset Flag

This bit is set if a Power-on Reset occurs. The bit is reset only by writing a '0' 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.