ATMEGA48V_11 ATMEL [ATMEL Corporation], ATMEGA48V_11 Datasheet - Page 54

• Manufacturer Part Number: ATMEGA48V_11
• Description: 8-bit Atmel Microcontroller with 4/8/16K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

2545T–AVR–05/11
If WDE is set, the watchdog timer is in interrupt and system reset mode. The first time-out in the
watchdog timer will set WDIF. Executing the corresponding interrupt vector will clear WDIE and
WDIF automatically by hardware (the watchdog goes to system reset mode). This is useful for
keeping the watchdog timer security while using the interrupt. To stay in interrupt and system
reset mode, WDIE must be set after each interrupt. This should however not be done within the
interrupt service routine itself, as this might compromise the safety-function of the watchdog sys-
tem reset mode. If the interrupt is not executed before the next time-out, a system reset will be
applied.
Table 11-1.
Note:
• Bit 4 - WDCE: Watchdog change enable
This bit is used in timed sequences for changing WDE and prescaler bits. To clear the WDE bit,
and/or change the prescaler bits, WDCE must be set.
Once written to one, hardware will clear WDCE after four clock cycles.
• Bit 3 - WDE: Watchdog system reset enable
WDE is overridden by WDRF in MCUSR. This means that WDE is always set when WDRF is
set. To clear WDE, WDRF must be cleared first. This feature ensures multiple resets during con-
ditions causing failure, and a safe start-up after the failure.
WDTON
1
1
1
1
0
1. WDTON fuse set to “0“ means programmed and “1“ means unprogrammed.
(1)
Watchdog timer configuration.
WDE
0
0
1
1
x
WDIE
0
1
0
1
x
Mode
Stopped
Interrupt mode
System reset mode
Interrupt and system reset
mode
System reset mode
ATmega48/88/168
Action on time-out
None
Interrupt
Reset
Interrupt, then go to system
reset mode
Reset
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