ATMEGA325-16AJ ATMEL [ATMEL Corporation], ATMEGA325-16AJ Datasheet - Page 44

• Manufacturer Part Number: ATMEGA325-16AJ
• Description: 8-bit Microcontroller with In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

Watchdog Timer Control
Register – WDTCR
44
ATmega325/3250/645/6450
Figure 21. Watchdog Timer
• Bits 7..5 – Res: Reserved Bits
These bits are reserved bits in the ATmega325/3250/645/6450 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. This
bit must also be set when changing the prescaler bits. See “Timed Sequences for
Changing the Configuration of the Watchdog Timer” on page 46.
• 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 follow-
ing procedure must be followed:
1. In the same operation, write a logic one to WDCE and WDE. A logic one must be
2. Within the next four clock cycles, write a logic 0 to WDE. This disables the
In safety level 2, it is not possible to disable the Watchdog Timer, even with the algo-
rithm described above. See “Timed Sequences for Changing the Configuration of the
Watchdog Timer” on page 46.
• Bits 2..0 – WDP2, WDP1, WDP0: Watchdog Timer Prescaler 2, 1, and 0
The WDP2, WDP1, and WDP0 bits determine the Watchdog Timer prescaling when the
Watchdog Timer is enabled. The different prescaling values and their corresponding
Time-out Periods are shown in Table 21 on page 45.
Bit
Read/Write
Initial Value
written to WDE even though it is set to one before the disable operation starts.
Watchdog.
R
7
–
0
OSCILLATOR
WATCHDOG
R
6
–
0
R
5
–
0
WDCE
R/W
4
0
WDE
R/W
3
0
WDP2
R/W
2
0
WDP1
R/W
1
0
WDP0
R/W
0
0
2570A–AVR–09/04
WDTCR