Datasheet

ATmega48A/PA/88A/PA/168A/PA/328/P
 2018 Microchip Technology Inc. Data Sheet Complete DS40002061A-page 63
11.9 Register Description
11.9.1 MCUSR – MCU Status Register
The MCU Status Register provides information on which reset source caused an MCU reset.
• Bit 7:4: Reserved
These bits are unused bits in the ATmega48A/PA/88A/PA/168A/PA/328/P, and will always read as zero.
• Bit 3 – WDRF: 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 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.
11.9.2 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 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 Timer is in Interrupt Mode, and the
corresponding interrupt is executed if time-out in the Watchdog Timer occurs. If WDE is set, the Watchdog
Timer is in Interrupt and System Reset Mode. The first time-out in the Watchdog Timer will set WDIF. Executing
Bit 76543210
0x34 (0x54)
––––WDRFBORFEXTRFPORFMCUSR
Read/Write R R R R R/W R/W R/W R/W
Initial Value0000 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