Operating System; Start-Up; Plc Cycle - WAGO 750-306 Technical Description

70 • Feldbus Coupler/Controller
Fieldbus Controller 750-806

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 initialization value given by the PLC program. The flags re-
tain their status. The "I/O" LED blinks red during this phase.
Following an error free start-up, the Controller changes over to the "RUN"
mode. The "I/O" LED lights up green.
A PLC program does not yet exist in the flash memory when delivered. The
Controller start-up is described without initializing the system. It then behaves
as a Coupler.

3.2.3.2 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.
WAGO-I/O-SYSTEM 750
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