Watchdog Timer Setting - IDEC SmartAXIS FT9Z-1A01 User Manual

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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 SmartAXIS requires
replacement.
Some of the reasons why a watchdog timer will occur are problems with the SmartAXIS 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.
For FBD, the watchdog timer cannot be reset in the program.
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 SmartAXIS 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
100ms and the maximum value for one scan is 120ms 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 SmartAXIS 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.
Watchdog Timer Settings
Select the watch dog timer setting between 100ms and 4000ms. The default time is 400ms.
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