Datasheet

15.6.1. MCUCSR – MCU Control and 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. The device is a complex microcontroller with more peripheral units than can be supported

within the 64 location reserved in Opcode for the IN and OUT instructions. For the Extended I/O space

from 0x60 in SRAM, only the ST/STS/STD and LD/LDS/LDD instructions can be used.

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

Note:

1. Only EXTRF and PORF are available in ATmega103 compatibility mode.

2. For Reset value, see bit description.

Name: MCUCSR

Offset: 0x34

Reset: 0x00

Property:

When addressing I/O Registers as data space the offset address is 0x54

Bit 7 6 5 4 3 2 1 0

JTRF WDRF BORF EXTRF PORF

Access

R/W R/W R/W R/W R/W

Reset - - - - -

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 – BORF: 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 MCUCSR 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.

Atmel ATmega64A [DATASHEET]

Atmel-8160E-ATmega64A_Datasheet_Complete-09/2015