SMC Networks 486DX4 - Manual (Page 49)

AR-B1462 User¡ ¦s Guide
5-9
5.3 WATCHDOG TIMER
This section describes how to use the Watchdog Timer, disabled, enabled, and trigger.
The AR-B1462 is equipped with a programmable time-out period watchdog timer. User can use the program to
enable the watchdog timer. 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. The time-out period can be programmed to be 3 to 42
seconds.
Watchdog
Register
Time Base
Counter
and
Compartor
Enable (D7)
Time Factor (D0-D2)
Write and Trigger
Watchdog
LED
RESET
Figure 5-1 Watchdog Block Diagram
5.3.1 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.
Time Factor Time-Out Period (Seconds)
80H 3
81H 6
82H 12
83H 18
84H 24
85H 30
86H 36
87H 42
Table 5-1 Time-Out Setting
If you want to generate IRQ15 signal to warn your program when watchdog times out, the following table listed the
relation of timer factors between time-out period. And if you use the IRQ15 signal to warn your program when
watchdog timer out, please enter the BIOS Setup the menu, the and Prefetch> these two items must set to Primary.
Time Factor Time-Out Period (Seconds)
0C0H 3
0C1H 6
0C2H 12
0C3H 18
0C4H 24
0C5H 30
0C6H 36
0C7H 42
Table 5-2 Time-Out Setting