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2.5.2 Using a watchdog timer for monitoring a user program
When you use the watchdog timer for monitoring the operational state of a user program,
the user program to be monitored must periodically retrigger the watchdog timer (that is,
reset the timeout counter of the watchdog timer to the initial value). Figure 2-1 shows an
example of monitoring the operational state of a user program.
Figure 2-1 Example of a Flow Chart of Monitoring the Operational State of a User Program
If a watchdog timer timeout occurs, that means the monitored program was not be able to
retrigger the watchdog timer within the configured timeout for some reasons.
A program can use a watchdog timer by calling the library function WdtControl. For
information about how to use the WdtControl function, see "6.1.3 Watchdog timer control
function (WdtControl)".
In addition, in the RAS Setup window, select "Retriggered by application program"
under Watchdog timer setting.
NOTE
• If you want to stop monitoring using the watchdog timer when a user program exits or
due to shutdown, you must stop the watchdog timer so that a timeout does not occur.
• If you select "Reset" or "Memory dump" for Action at timeout under Watchdog
timer setting in the RAS Setup window, the time it takes to generate timeout is
longer than the timeout value set by the application. This is a correct operation.
This situation occurs because it takes about 1.2 to 1.3 seconds for the hardware timer
on this equipment to actually enable the timeout setting set by the application. If the
timeout is set to 30 seconds, reset or memory dump starts about 31 seconds after the
timeout is set.
2. ITEMS MONITORED BY THE RAS FEATURE
Monitored program
Process a user-defined
routine
Trigger the
watchdog timer
Retrigger
Equipment
Watchdog timer
2-5
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