ATTINY15 ATMEL [ATMEL Corporation], ATTINY15 Datasheet - Page 34

• Manufacturer Part Number: ATTINY15
• Manufacturer: ATMEL [ATMEL Corporation]

The Watchdog Timer
The Watchdog Timer Control
Register – WDTCR
34
ATtiny15L
The Watchdog Timer is clocked from a separate On-chip Oscillator that runs at 1 MHz.
This is the typical value at V
values at other V
Reset interval can be adjusted from 16 to 2048 ms, as shown in Table 15. The WDR
(Watchdog Reset) instruction resets the Watchdog Timer. Eight different clock cycle
periods can be selected to determine the reset period. If the reset period expires without
another Watchdog Reset, the ATtiny15L resets and executes from the reset vector. For
timing details on the Watchdog Reset, refer to page 17.
To prevent unintentional disabling of the Watchdog, a special turn-off sequence must be
followed when the Watchdog is disabled. Refer to the description of the Watchdog Timer
Control Register for details.
Figure 23. Watchdog Timer
• Bits 7..5 – Res: Reserved Bits
These bits are reserved bits in the ATtiny15L and will always read as zero.
• Bit 4 – WDTOE: Watchdog Turn-off Enable
This bit must be set (one) when the WDE bit is cleared. Otherwise, the Watchdog will
not be disabled. Once set, hardware will clear this bit to zero after four clock cycles.
Refer to the description of the WDE bit for a Watchdog disable procedure.
• Bit 3 – WDE: Watchdog Enable
When the WDE is set (one), the Watchdog Timer is enabled and if the WDE is cleared
(zero), the Watchdog Timer function is disabled. WDE can be cleared only when the
WDTOE bit is set (one). To disable an enabled Watchdog Timer, the following proce-
dure must be followed:
1. In the same operation, write a logical “1” to WDTOE and WDE. A logical “1” must
2. Within the next four clock cycles, write a logical “0” to WDE. This disables the
Bit
$21
Read/Write
Initial Value
be written to WDE even though it is set to one before the disable operation starts.
Watchdog.
R
7
–
0
WATCHDOG
CC
RESET
levels. By controlling the Watchdog Timer prescaler, the Watchdog
1 MHz at Vcc = 5V
350 KHz at Vcc = 3V
WDP0
WDP1
WDP2
WDE
R
6
–
0
Oscillator
CC
= 5V. See “Typical Characteristics” on page 66 for typical
R
5
–
0
WDTOE
R/W
4
0
WDE
R/W
3
0
PRESCALER
WATCHDOG
MCU RESET
WDP2
R/W
2
0
WDP1
R/W
1
0
WDP0
R/W
0
0
1187D–12/01
WDTCR