Datasheet

ATmega640/1280/1281/2560/2561

2549K–AVR–01/07

MCUSR – MCU Status

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

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 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.

WDTCSR – Watchdog Timer

Control Register

• Bit 7 - WDIF: Watchdog Interrupt Flag

This bit is set when a time-out occurs in the Watchdog Timer and the Watchdog Timer is

configured for interrupt. WDIF is cleared by hardware when executing the corresponding

interrupt handling vector. Alternatively, WDIF is cleared by writing a logic one to the flag.

When the I-bit in SREG and WDIE are set, the Watchdog Time-out Interrupt is

executed.

• Bit 6 - WDIE: Watchdog Interrupt Enable

When this bit is written to one and the I-bit in the Status Register is set, the Watchdog

Interrupt is enabled. If WDE is cleared in combination with this setting, the Watchdog

Bit 76543210

0x35 (0x55)

– – – JTRF WDRF BORF EXTRF PORF MCUSR

Read/Write R R R R/W R/W R/W R/W R/W

Initial Value 0 0 0 See Bit Description

Bit 76543210

(0x60) WDIF WDIE WDP3 WDCE WDE WDP2 WDP1 WDP0 WDTCSR

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value0000X000