ATTINY12 ATMEL Corporation, ATTINY12 Datasheet - Page 24

• Manufacturer Part Number: ATTINY12
• Description: 8-bit AVR Microcontroller with 1K Byte Flash
• Manufacturer: ATMEL Corporation

MCU Status Register –
MCUSR for the ATtiny12
ATtiny12 Internal Voltage
Reference
Voltage Reference Enable
Signals and Start-up Time
24
ATtiny11/12
before the bits are cleared. If the bit is cleared before an external or watchdog reset
occurs, the source of reset can be found by using the following truth table:
Table 12. Reset Source Identification
The MCU 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 ATtiny12 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 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 by writing a logic zero to the
flag.
To use 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.
ATtiny12 features an internal voltage reference with a nominal voltage of 1.22V. This
reference is used for Brown-out Detection, and it can be used as an input to the Analog
Comparator.
The voltage reference has a start-up time that may influence the way it should be used.
The maximum start-up time is 10µs. To save power, the reference is not always turned
on. The reference is on during the following situations:
Bit
$34
Read/Write
Initial Value
EXTRF
0
1
0
1
R
7
0
-
R
6
0
-
PORF
R
0
0
1
1
5
0
-
R
4
0
-
Reset Source
Watchdog Reset
External Reset
Power-on Reset
Power-on Reset
WDRF
R/W
3
See Bit Description
BORF
R/W
2
EXTRF
R/W
1
PORF
R/W
1006D–AVR–07/03
0
MCUSR