Rockwell Automation Logix5000 Controllers Tasks, Programs, and Routines Programming Manual - Manual (Page 32)

Chapter 1 Manage tasks
4. Use either Run Continuous Task (default) or Reserve for System Tasks.
• Select the Run Continuous Task radio button when there are no
communication or background tasks to process; the controller
immediately returns to the continuous task.
• Select the Reserve for System Task radio button to allocate the entire
1 ms of the system-overhead time slice when the controller has
communication or background tasks to perform before returning to the
continuous task. This lets you simulate a communication load on the
controller during design and programming before HMIs, controller to
controller messaging, and so forth, are set up. Use this setting for testing
purposes only.
5. Click OK.
Each task contains a watchdog timer that specifies how long a task can run before
triggering a major fault.
If the watchdog timer reaches a configurable preset, a major fault occurs. Depending on the controller fault
handler, the controller might shut down.
• A watchdog time can range from 1…2,000,000 ms (2000 seconds). The
default is 500 ms.
• The watchdog timer begins to run when the task is initiated and stops when
all the programs within the task have run.
• If the task takes longer than the watchdog time, a major fault occurs. The
time includes interruptions by other tasks.
• You can use the controller fault handler to clear a watchdog fault. If the
same watchdog fault occurs a second time during the same logic scan, the
controller enters Faulted mode, regardless of whether the controller fault
handler clears the watchdog fault.
Adjust the system
watchdog time
32 Rockwell Automation Publication 1756-PM005-EN-P - October 2014