Overview Of The Most Important Task Priorities; System Events - WAGO 750 Series Manual

96 • Fieldbus Controller 750-841
Programming the PFC with WAGO-I/O-PRO CAA
3.1.8.2.2 Overview of the Most Important Task Priorities (descending priority)
• I/O Bus Task / Fieldbus Task ( Internal ):
• Normal Task ( IEC-Tasks 1-10 ):
• PLC Comm Task (Internal):
• Background Task ( IEC-Tasks 11-31 ):
More information
For detailed information on the programming tool WAGO-I/O-PRO CAA,
please refer to the WAGO-I/O-PRO CAA manual. An electronic copy of this
manual can be found on WAGO's web site:

3.1.8.2.3 System Events

The I/O Bus task is an internal task, which updates the I/O module data
from the process image.
Fieldbus tasks are triggered by fieldbus events (communications); therefore,
they only use processing time when the fieldbus is active.
IEC tasks with these priorities can be interrupted by the I/O Bus and
Fieldbus tasks. Therefore, if the watchdog is used, before selecting the
sampling rate, consider the number of I/O modules in the node and the
communication activity via the fieldbus.
The PLC Comm Task is only active when you are logged in with CoDeSys.
This task manages the communication with the CoDeSys-Gateway.
All internal tasks have a higher priority than the IEC background tasks.
Therefore, IEC background tasks are used for time-consuming and time-
uncritical jobs (e.g., SysLibFile functions)
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