Axiomtek FDK172-834 User Manual download pdf (Page 65)

FDK172-834 User’s Manual

Watchdog Timer 59

Appendix A

Watchdog Timer

About Watchdog Timer

Software stability is major issue in most application. Some embedded systems are not

watched by human for 24 hours. It is usually too slow to wait for someone to reboot when

computer hangs. The systems need to be able to reset automatically when things go wrong.

The watchdog timer gives us solution.

The watchdog timer is a counter that triggers a system reset when it counts down to zero from

a preset value. The software starts counter with an initial value and must reset it periodically. If

the counter ever reaches zero which means the software has crashed, the system will reboot.

How to Use Watchdog Timer

The I/O port base addresses of watchdog timer are 2E (hex) and 2F (hex). The 2E (hex) and

2F (hex) are address and data port respectively.

Assume that program A is put in a loop that must execute at least once every 10ms. Initialize

watchdog timer with a value bigger than 10ms. If the software has no problems; watchdog

timer will never expire because software will always restart the counter before it reaches zero.

Begin

Enable and Initialize

Watchdog Timer

Program “A”

Disable Watchdog

Timer

Begin

Enable and Initialize

Watchdog Timer

Program “A”

Reset Watchdog

Timer

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Axiomtek FDK172-834 User Manual Page 65