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AR-B1474 User¡ ¦ s Guide
4.4 WATCHDOG TIMER
This section describes how to use the Watchdog Timer, disabled, enabled, and trigger.
The AR-B1474 is equipped with a programmable time-out period watchdog timer. This watchdog timer can be
enabled by your program. Once you have enabled the watchdog timer, the program should trigger it every time
before it times out. If your program fails to trigger or disable this timer before it times out because of system hang-
up, it will generate a reset signal to reset the system or generate the IRQ15 signal to tell your program that the
watchdog is times out. The time-out period can be programmed to be 6 to 42 seconds.
4.4.1 Watchdog Timer Setting
The watchdog timer is a circuit that may be used from your program software to detect crashes or hang-ups.
Whenever the watchdog timer is enabled, the LED will blink to indicate that the timer is counting. The watchdog
timer is automatically disabled after reset.
Once you have enabled the watchdog timer, your program must trigger the watchdog timer every time before it
times-out. After you trigger the watchdog timer, it will be set to zero and start to count again. If your program fails
to trigger the watchdog timer before time-out, it will generate a reset pulse to reset the system or trigger the IRQ15
signal to tell your program that the watchdog is times out.
The factor of the watchdog timer time-out constant is approximately 6 seconds. The period for the watchdog timer
time-out period is between 1 to 7 timer factors.
If you want to reset your system when watchdog times out, the following table listed the relation of timer factors
between time-out period.
Table 4-1 Time-Out Setting
4-6
Enable (D6, D7)
Time Factor (D0-D2)
Write and Trigger
Figure 4-1 Watchdog Block Diagram
Time Factor
80H
81H
82H
83H
84H
85H
86H
87H
Time Base
Watchdog
Register
Compartor
Watchdog
LED
Time-Out Period (Seconds)
3
6
12
18
24
30
36
42
Counter
and
RESET
IRQ15
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