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ManualsBrandsMICROCHIP TECHNOLOGY ManualsMicrocontrollers, Microprocessors & QuartzesEmbedded microcontroller TQFP 32 (7x7) 8-Bit 16 MHz I/O number 23
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ATmega8A [DATASHEET]
8159E–AVR–02/2013
11.6 Register Description
11.6.1 MCUCSR – MCU Control and Status Register
The MCU Control and Status Register provides information on which reset source caused an MCU Reset.
• Bit 7:4 – Res: Reserved Bits
These bits are reserved bits in the ATmega8A and always read as zero.
• 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.
11.6.2 WDTCR – Watchdog Timer Control Register
• Bits 7:5 – Res: Reserved Bits
These bits are reserved bits in the ATmega8A and will always read as zero.
• Bit 4 – WDCE: Watchdog Change Enable
This bit must be set when the WDE bit is written to logic zero. Otherwise, the Watchdog will not be disabled. Once
written to one, hardware will clear this bit after four clock cycles. Refer to the description of the WDE bit for a
Watchdog disable procedure. In Safety Level 1 and 2, this bit must also be set when changing the prescaler bits.
See the Code Examples on page 40.
• Bit 3 – WDE: Watchdog Enable
When the WDE is written to logic one, the Watchdog Timer is enabled, and if the WDE is written to logic zero, the
Watchdog Timer function is disabled. WDE can only be cleared if the WDCE bit has logic level one. To disable an
enabled Watchdog Timer, the following procedure must be followed:
Bit 76543210
– – – – WDRF BORF EXTRF PORF MCUCSR
Read/Write R R R R R/W R/W R/W R/W
Initial Value 0 0 0 0 See Bit Description
Bit 76543210
– – – WDCE WDE WDP2 WDP1 WDP0 WDTCR
Read/Write R R R R/W R/W R/W R/W R/W
Initial Value00000000