ATMEGA128-16AU SL383 Atmel, ATMEGA128-16AU SL383 Datasheet - Page 56

• Manufacturer Part Number: ATMEGA128-16AU SL383
• Manufacturer: Atmel

Watchdog Timer
Control Register –
WDTCR
56
ATmega128
Table 21. WDT Configuration as a Function of the Fuse Settings of M103C and WDTON.
Figure 28. Watchdog Timer
• Bits 7..5 – Res: Reserved Bits
These bits are reserved bits in the ATmega128 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. In Safety Level 1 and 2, this bit
must also be set when changing the prescaler bits.
Configuration of the Watchdog Timer” on page 58.
• 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 following procedure must be
followed:
Bit
Read/Write
Initial Value
M103C
Unprogrammed
Unprogrammed
Programmed
Programmed
R
7
–
0
WDTON
Unprogrammed
Programmed
Unprogrammed
Programmed
R
6
–
0
OSCILLATOR
WATCHDOG
R
5
–
0
Safety
Level
1
2
0
2
WDCE
R/W
4
0
WDT Initial
State
Disabled
Enabled
Disabled
Enabled
WDE
R/W
3
0
See “Timed Sequences for Changing the
WDP2
R/W
2
0
How to Disable
the WDT
Timed
sequence
Always enabled
Timed
sequence
Always enabled
WDP1
R/W
1
0
WDP0
R/W
0
0
How to
Change
Time-out
Timed
sequence
Timed
sequence
No
restriction
Timed
sequence
WDTCR
2467S–AVR–07/09