Pfc Cycle - WAGO I/O SYSTEM 750 750-833 Manual

3.3.2 PFC Cycle

The PFC cycle starts following a fault free run-up when the operating mode
switch is in the top position or by a start command from the WAGO-I/O-
PRO. The input and output data of the field bus and the I/O modules as well as
the times are read. Subsequently the PFC user program in the RAM is
processed followed by the output data of the field bus and the I/O modules in
the process image . Operating system functions, amongst others, for
diagnostics and communication are performed and the time is actualized at the
end of the PFC 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 PFC
cycle.
The cycle time is the time from the start of the PFC user program to the next
start. If a loop is programmed within a PFC user program the PFC run time
and thus the PFC cycle are extended correspondingly.
The inputs, outputs and times are not updated during the processing of the
PLC program. This actualization 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.
WAGO-I/O-SYSTEM 750
Bus System
Programmable Field Bus Controller 750-833
Operating System
• 59