Rainbow Electronics ATmega128L - Manual (Page 49)

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ATmega128(L)
2467B–09/01
Figure 26. Watchdog Reset During Operation
MCU Control and Status
Register – MCUCSR The MCU Control and Status Register provides information on which reset source
caused an MCU reset.
Note that only EXTRF and PORF are available in ATmega103 compatibility mode.
• 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 writ-
ing 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 writ-
ing 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 writ-
ing 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.
Internal Voltage
Reference ATmega128 features an internal bandgap reference. This reference is used for Brown-
out Detection, and it can be used as an input to the Analog Comparator or the ADC. The
2.56V reference to the ADC is generated from the internal bandgap reference.
CK
CC
Bit 7 6 5 4 3 2 1 0
JTD - - JTRF WDRF BORF EXTRF PORF MCUCSR
Read/Write R/W R R R/W R/W R/W R/W R/W
Initial value 0 0 0 See bit description