WAGO-I/O-SYSTEM 750
Programming the PFC Using WAGO-I/O-PRO 103
750-806 Fieldbus Controller DeviceNet
TM
Manual
Version 2.0.0
9.3.1
IEC Task Sequence
1.
Determine the system time (tStart).
2.
If no full internal bus cycle has run since the last time the outputs were
written:
Wait until the next internal bus cycle is completed.
3.
Reading of inputs and reading back of the outputs from the process image.
4.
If the application program has been started.
Execute the program codes for this task.
5.
Writing of the outputs to the process image.
6.
Determine the system time (tEnd).
tEnd - tStart = runtime for the IEC task
9.3.2
Overview of Most Important Task Priorities
Table 40: Task Processing
Task
Importance of the execution
Internal bus task, fieldbus task
of priority before all others
Normal task
after the internal bus and fieldbus tasks
PLC-Comm task
after the normal tasks
Background task
after the PLC-Comm tasks
Internal bus task/fieldbus task (internal)
The internal bus task matches the process image to the input/output data of the
modules in defined cycles. The fieldbus tasks are performed as triggered by
events and only require computing time when communication is performed via
fieldbus (MODBUS).
Normal task (IEC-Task priorities 1-10 that can be set in CODESYS)
IEC tasks with this priority may be interrupted by the internal bus tasks.
Therefore, configuration for the connected modules and communication via
fieldbus with the watchdog activated for the task call interval must be taken into
account here.
PLC-Comm task (internal)
The PLC-Comm task is active when logged in and takes up communication with
the CODESYS gateway.
Background task (IEC-Task priorities 11-31 that can be set in CODESYS)
All internal tasks have a priority higher than that for the IEC background tasks.
These tasks are therefore very well-suited for performing time-intensive and non-
critical time tasks, such as calling up functions in the SysLibFile.lib.
