Watchdog Timer Setting - IDEC MICROSmart FC6A Series User Manual

5: F S
UNCTIONS AND ETTINGS

Watchdog Timer Setting

This section describes watchdog timer setting.
A watchdog error occurs when the processing time for one scan exceeds the allowed time while the user program is running.
If a watchdog error occurs, the system is reset with the purpose of returning the system to normal operation.
If the watchdog error occurs frequently, you can assume that there is a hardware problem and that the FC6A Series MICROSmart
requires replacement.
Some of the reasons why a watchdog timer will occur are problems with the FC6A Series MICROSmart hardware and length of the
processing time in the program. If the processing time for one scan of the ladder program exceeds the time configured for the
watchdog timer on the ladder program, place an NOP (no operation) instruction in the ladder program. The watchdog timer is
reset when the NOP instruction is executed.
Watchdog timer setting time
The watchdog timer setting time can be changed in the Function Area Settings. Decide on the watchdog timer setting time in
either of the following two ways.
Decide by user system specification

Determine the maximum on time (milliseconds) so the output signals do not stay on if the FC6A Series MICROSmart loses
control and set that value as the watchdog timer setting time. However, if the ladder program processing time takes longer than
the design specification, use an NOP (no operation) instruction in the ladder program. For example, when the watchdog timer is
set to 100 ms and the maximum value for one scan is 120 ms on the ladder program, insert an NOP instruction in the ladder
program to ensure that the error does not occur.
Match the program processing time

Check the maximum value for one scan (D8024) and set the watchdog timer value as a value with a safety margin added to the
maximum value.
Note: When changing the watchdog timer setting value, select an appropriate value that fully takes into consideration the safety of the system.
The maximum value of one scan while the FC6A Series MICROSmart is running can be checked with special data register D8024.
Programming WindLDR
Select Configuration from the WindLDR menu bar, and then click Self Diagnostic.
1.
The Function Area settings dialog box appears.
Select the watchdog timer setting value.
2.
Click OK.
3.
This concludes configuring the settings.
Watchdog Timer Settings
Select the watch dog timer setting between 100 ms and 4,000 ms. The default time is 400 ms.
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