ATTINY12 ATMEL Corporation, ATTINY12 Datasheet - Page 23

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

Watchdog Reset
MCU Status Register –
MCUSR of the ATtiny11
1006D–AVR–07/03
When the Watchdog times out, it will generate a short reset pulse of 1 CK cycle dura-
tion. On the falling edge of this pulse, the delay timer starts counting the Time-out period
(t
Figure 22. Watchdog Reset during Operation
The MCU Status Register provides information on which reset source caused an MCU
reset.
• Bit 7..2 - Res: Reserved Bits
These bits are reserved bits in the ATtiny11 and always read as zero.
• Bit 1 - EXTRF: EXTernal Reset Flag
After a power-on reset, this bit is undefined (X). It will be set by an external reset. A
watchdog reset will leave this bit unchanged.
• Bit 0 - PORF: Power-on Reset Flag
This bit is set by a power-on reset. A watchdog reset or an external reset will leave this
bit unchanged.
To summarize, the following table shows the value of these two bits after the three
modes of reset.
Table 11. PORF and EXTRF Values after Reset
To identify a reset condition, the user software should clear both the PORF and EXTRF
bits as early as possible in the program. Checking the PORF and EXTRF values is done
Bit
$34
Read/Write
Initial Value
TOUT
Reset Source
Power-on
External Reset
Watchdog Reset
). Refer to page 36 for details on operation of the Watchdog.
V
CC
R
7
0
-
R
6
0
-
R
5
0
-
CK
R
4
0
-
Unchanged
Undefined
EXTRF
1
R
3
0
-
R
2
0
-
EXTRF
See bit description
ATtiny11/12
R/W
1
Unchanged
Unchanged
PORF
PORF
R/W
1
0
MCUSR
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