Rainbow-electronics ATmega8HVD Manuel d'utilisateur télécharger pdf (Page 48)

8052B–AVR–09/08

ATmega4HVD/8HVD

10.8 Register Description

10.8.1 MCUSR – MCU Status Register

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

• Bits 7:4, 2 – Res: Reserved Bits

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

• Bit 4 – OCDRF: OCD Reset Flag

This bit is set if a debugWIRE Reset occurs. This bit is reset by a Power-on Reset, or by writ-

ing 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 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.

10.8.2 WDTCSR – Watchdog Timer Control Register

• Bit 7 - WDIF: Watchdog Interrupt Flag

This bit is set when a timeout occurs in the Watchdog Timer and the Watchdog Timer is con-

figured 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 Timeout 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 Timer is in Inter-

rupt Mode, and the corresponding interrupt is executed if timeout in the Watchdog Timer

occurs.

Bit 7 6 5 4 3 2 1 0

– – – OCDRF WDRF – EXTRF PORF MCUSR

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

Initial Value 0 0 0 0 (1) 0 (1) (1)

Bit 76543210

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 Value 0 0 0 0 X 0 0 0

1 2 ... 43 44 45 46 47 48 49 50 51 52 53 ... 167 168

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Rainbow-electronics ATmega8HVD Manuel d'utilisateur Page 48