General Information About Iec Tasks - WAGO -I/O-SYSTEM 750 Manual

WAGO-I/O-SYSTEM 750
750-882 Media Redundancy ETHERNET Controller
9.4

General Information about IEC Tasks

Please note the following information when programming your IEC tasks:
Use different priorities for IEC tasks!
Give IEC tasks (in WAGO-I/O-PRO under the Resources tab > Task
Configuration) different priorities to prevent an error from occurring when
compiling the user program.
An interruption of IEC tasks is possible through tasks of higher priority!
An ongoing task may be interrupted by tasks with higher priorities. Execution of
the task that has been interrupted is resumed only when there are no other
higher-priority tasks to be executed.
Distortion of variables in overlapping areas of the process image!
If several IEC tasks utilize input or output variables with the same, or overlapping
addresses in the process image, the values for the input or output variables may
change while the IEC task is being executed!
Observe waiting periods of free-running tasks!
Running tasks are halted after each task cycle for half the time that the task
proper requires (min. 1 ms). Execution of the task is then resumed.
Example:
The default task is created by default!
If no task has been defined in the task configuration, a running default task is
created during translation. This task, called "Default task", is recognized by this
name in the firmware, meaning that the name "Default task" cannot be used for
other task names.
Observe the watchdog sensitivity for cyclic tasks!
The watchdog sensitivity indicates how many times the watchdog time is
exceeded for an even to be triggered. You set the sensitivity in WAGO-I/O-PRO
under Register Resources > Task Configuration for Cyclical Tasks. The values
1 and 0 are equivalent with regard to sensitivity. A sensitivity value of 0 or 1
results in the watchdog event being triggered when the watchdog time is
exceeded on time. With a sensitivity value of 2, for instance, the watchdog time
must be exceeded in two consecutive task cycles in order for the watchdog event
to be triggered.
Programming the PFC Using WAGO-I/O-PRO 137
st
1 Task 4 ms  Waiting period 2 ms
nd
2 Task 2 ms  Waiting period 1 ms
Manual
1.5.0