Moeller XION-PLC-CANopen, Hardware, Engineering And Function Description

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Using the XN-PLC
02/05 AWB2724-1566GB
18
Program start
When a program starts, the XN-PLC checks whether the
configured inputs and outputs match the physically present ones.
It also checks whether the actual module corresponds with the
parameterized module type. If the wrong module type is identified,
the CPU changes to NOT READY state. If no module is connected,
the start-up procedure continues.
Program start (STOP l RUN)
You can start the program in one of two ways:
• In online operation, issue the START command, for example
after loading a program. The CPU must be in STOP state and the
operating mode switch in the RUN position.
• Set the operating mode switch to its RUN position.
Behaviour after power off or power interruption
If you switch off or interrupt the CPU power while a program is
running, the program cycle or the task is interrupted immediately,
so that data integrity is no longer given. All outputs are set to 0 or
switched off.
table 6 on page 18 shows the behaviour of retentive variables.
The remaining program cycle will not be completed when power is
reconnected!
If inconsistent data is not acceptable in your application, you can,
for example, use an uninterruptible power supply (UPS).
The PLC restarts as defined by the settings in the PLC
Configuration window, a figure 16.
Program stop (RUN l STOP)
When you set the operating mode switch to STOP, the CPU
changes to STOP state, as soon as the program cycle is completed.
The outputs are set to 0.
You can stop the program in one of two ways:
• In online operation, issue the STOP command.
• Set the operating mode switch to its STOP position.
Table 6: Behaviour of the variables at PLC start
Program processing and system time
The user program is processed cyclically. The states of the inputs
are read before the start of each program cycle, and the output
states are written to the outputs at the end of the cycle.
The run-time system’s software architecture can cause timing jitter
between individual processing cycles.
You can also program application routines that are started by the
occurrence of system events;
a section “System events” on
page 20.
Monitoring cycle time
A hardware timer monitors the cycles of the user program and the
individual event tasks. If the cycle time exceeds a user-defined
value, the PLC goes into STOP state and the outputs are switched
off.
You can specify the timeout value on the Other Parameters tab
in the PLC Configuration window between 20 ms (default value)
and 1000 ms.
Start-up condition Variable type
Non-retentive Retentive
COLDSTART Initial values are loaded
WARMSTART Initial values are
loaded Values
remain in
memory
Program loaded and started in
online operation Initial values are loaded
Start/Stop/Start... Values remain in memory
h You can not declare physical operands, such as I, Q and
M, as retentive variables.