IPC Solutionki PC104-386L-2M, User Manual, Page: 43 / 69

NAGASAKI Corporation
4.3 WATCHDOG TIMER
This section describes how to use the Watchdog Timer, disabled, enabled, and trigger.
The
PC104-386L-2M 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 or trigger an IRQ signal. The time-out period can be programmed to be
30.5
μ
seconds to 512 seconds.
Watchdog
Register
Time Base
Counter
and
Compartor
Software Program
Enable and Trigger
Write and Trigger
RESET
Figure 4-1 Watchdog Block Diagram
Watchdog Timer Setting
The watchdog timer is a circuit that may be used from your program software to detect
crashes or hang-ups. 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 an IRQ signal to tell your program that the
watchdog is times out.
Watchdog timer -INDEX 39H, 3AH, and 3BH
3Bh 3Ah 39h
D7…D0 D7…D0 D7…D0
Counter [MSB …LSB]
For example
INDEX 3Bh 3A
h
39h
00h 00h 01h 30.5
μ
sec
-- -- 02h 61
μ
sec
00h 01h 00h 7.8 m sec
00h 02h 00h 15.6 m sec
01h 00h 00h 2 sec
02h 00h 00h 4 sec
FFh FFh FFh 512 sec
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