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Fieldbus coupler/controller
Review
L
ON
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ORKS
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3.2.4.2 PLC cycle
The PLC cycle starts following an error free start-up when the operating mode
switch is in the top position or by a start command from the
WAGO-I/O-
PRO
32. The input and output data of the fieldbus and the I/O
modules as well as the times are read. Subsequently the PLC program in the
RAM is processed followed by the output data of the fieldbus and the I/O
modules in the process image. Operating system functions, amongst others, for
diagnosis and communication are performed and the times are updated at the
end of the PLC cycle. The cycle starts again with the reading in of the input
and output data and the times.
The change of the operating mode (STOP/RUN) is made at the end of a PLC
cycle.
The cycle time is the time from the start of the PLC program to the next start.
If a loop is programmed within a PLC program, the PLC running time and
thus the PLC cycle are extended correspondingly.
The inputs, outputs and times are not updated during the processing of the
PLC program. This update occurs in a defined manner only at the end of the
PLC program. For this reason it is not possible to wait for an event from the
process or the elapse of a time within a loop.