Watchdog Timer Operation - Fujitsu MB90390 Series Hardware Manual

12.2

Watchdog Timer Operation

The watchdog timer function enables detection of program surge.
If the watchdog timer is not accessed within the specified time due to, for example, a
program surge, the watchdog timer resets the system.
■ State Transition Diagram of the Watchdog Timer
The watchdog timer has four states:
Inactive:
Running: The watchdog counter is counting up from "0".
Stopped:
Overflow: The watchdog counter asserts a watchdog reset.
Figure 12.2-1 State Transition Diagram of the Watchdog Timer
Inactive
(Initial State)
Write "0"
to WTE
Running
Start counting from 0
Write "0" to WTE
The watchdog timer does not operate.
The watchdog counter is stopped at count value "0".
Reset
Release of stop mode by interrupt
Release of time-base timer mode by interrupt
Release of sleep mode by interrupt
Transition to stop mode
Transition to time-base timer mode
Transition to sleep mode
Counter
overflow
Reset
Overflow
Assert watchdog reset
CHAPTER 12 WATCHDOG TIMER
Stopped
count = 0
Always
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