54 • Fieldbus controller 750-842
Operating system
Modular I/O System
ETHERNET TCP/IP
3.2.3 Operating
system
3.2.3.1 Start-up
The controller starts-up after switching on the supply voltage or after a hard-
ware reset. The PLC program in the flash memory is transferred to the RAM.
This is followed by the initialization of the system. The controller determines
the I/O modules and the present configuration. The variables are set to 0 or to
FALSE or to an initial value given by the PLC program. The flags retain their
status . The "I/O" LED blinks red during this phase.
Following a fault free start-up the controller changes over to the "RUN" mode.
The "I/O" LED lights up green.
There is not a PLC program in the flash memory when delivered. The control-
ler start-up as described, without initialiing the system. Then it behaves as a
coupler
3.2.3.2 PLC
cycle
The PLC cycle starts following a fault 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
diagnostics and communications are performed and the times calculated at the
end of the PLC cycle. The cycle starts again with the reading 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 calculation 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.