Lenze PLC Designer PLC Designer (R3-1) - Manual (Page 752)

L-force | PLC Designer
General Editors
750 DMS 4.1 EN 03/2011 TD29
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Processing order of elements in a sequence (matching the processing order as used in
»PLC Designer« V2.3):
1. Reset All action control flags of the IEC actions get re-set (not however the flags of IEC
actions that are called within actions!).
2. Step Exit Actions All steps are checked in the order which they assume in the sequence chart (top to
bottom and left to right) to determine whether the requirement for execution of
the step exit action is provided, and - if that is the case - this will be executed. An
exit action will be executed, if the step is going to get deactivated, that is if its
entry and step actions - if existing - have been executed during the last cycle, and
if the transition for the following step is TRUE.
3. Step Entry
Actions All steps are tested in the order which they assume in the sequence to determine
whether the requirement for execution of the step entry action is provided and - if
that is the case - this will be executed. An entry action will be executed, if the step-
preceding transition condition is TRUE and thus the step has been activated.
4. Timeout check,
Step Active Actions For all steps , the following is done in the order which they assume in the
sequence:
- (not yet implemented) If applicable, the elapsed time is copied into the
corresponding implicit step status variable .t
- (not yet implemented) If applicable, any timeout is tested and the SFC error flags
are serviced as required.
- For non-IEC steps, the corresponding step active action is now executed.
5. IEC Actions IEC actions that are used in the sequence are executed in alphabetical order. This is
done in two passes through the list of actions. In the first pass, all the IEC actions
that are deactivated in the current cycle are executed. In the second pass, all the
IEC actions that are active in the current cycle are executed.
6. Transition check,
Activating next
steps Transitions are evaluated: If the step in the current cycle was active and the
following transition returns TRUE (and if applicable the minimum active time has
already elapsed), then the following step is activated.
Note:
The following must be noticeed concerning implementation of actions:
It can come about that an action is carried out several times in one cycle because it is
associated with multiple sequences. (For example, an SFC could have two IEC actions
A and B, which are both implemented in SFC, and which both call IEC action C; then
in IEC actions A and B can both be active in the same cycle and furthermore in both
actions IEC action C can be active; then C would be called twice).
If the same IEC action is used simultaneously in different levels of an SFC, this could
lead to undesired effects due to the processing sequence described above. For this
reason, an error message is issued in this case. It can possibly arise during processing
of projects created with older versions of the programming system.
Note: Notice the possibility of using implicit variables for controlling the status of
steps and actions resp. the execution of the chart.