ATmega16HVB datasheet(49/273 Pages) ATMEL

49 / 273 page

8042A–AVR–07/09

ATmega16HVB/32HVB

11.5

11.5.1

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 ATmega16HVB/32HVB, and will always read as zero.

• Bit 4 – OCDRF: OCD Reset Flag

This bit is set if a debugWIRE Reset occurs. The 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. In the case of a Power-on Reset, both the BODRF

and the PORF will be set. The BODRF is reset 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.

11.5.2

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 config-

ured 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

543210

0x34 (0x54)

–

OCDRF

WDRF

BODRF

EXTRF

PORF

MCUSR

Read/Write

R/W

Initial Value

See Bit Description

Bit

765

432

(0x60)

WDIF

WDIE

WDP3

WDCE

WDE

WDP2

WDP1

WDP0

WDTCSR

Read/Write

R/W

Initial Value

ATmega16HVB Datenblatt(PDF) 49 Page - ATMEL Corporation

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