Lenze DDS v2.3 - Manual (Page 51)

Drive PLC Developer Studio
Programming languages
4-13
l
DDS EN 2.3
In a control cycle, all actions belonging to active steps are being executed. The subsequent
transition condition is checked once an active step has been executed. If the transition condition
is met (TRUE), the subsequent step will be executed during the next control cycle.
Step flag
Each step has a flag to save the step status.
Note!
A step flag bears the step’s name.
A step and a Boolean variable must not bear the same name as logical errors may otherwise occur.
•
The flag does not need to be explicitly declared.
•
The step flag (active or inactive step status) is represented by the logical value of a Boolean
variable <StepName>.
•
This Boolean variable has a value TRUE if the associated step is active, and FALSE if it is not.
This variable is implicitly declared and can be used in any action and transition of the SFC
organization unit.
Time flag
The active time of a step can be interrogated via flag _time <StepName>.
•
The flag does not need to be explicitly declared.
•
Interrogation works only if a minimum time was set in the step attributes for the step to be
interrogated, for example t#0ms.
4.4.6 IEC step
SFC also offers standard-compliant IEC steps in addition to the simplified steps.
Include the SFC library iecsfc.lib into your project to use IEC steps.
An IEC step can be assigned any number of actions.
•
Unlike simplified steps, IEC actions are not firmly assigned to a step as an entry or exit action,
but are available separately from the steps and can be applied more than once within their
organization unit. For this purpose, IEC actions must be linked with the desired steps with the
help of command Extras
➞ ➞ ➞ ➞Associate action.
Not only actions but also Boolean variables can be assigned to steps.
•
So-called qualifiers control activation and deactivation of actions and Boolean variables, also
permitting time delays.
•
Concurrences may occur since an action may still be active even if the next step may already
be processed, via qualifier S (Set), for example.
Associated Boolean variables are set or reset on each SFC organization unit call, i. e. it is reassigned
either the value TRUE or FALSE each time.
The actions associated with an IEC step are displayed in a split box to the right of the step. The
left-hand field contains the qualifier (if necessary with time constants), the right-hand field the name
of the action or the Boolean variable.
Show/Hide Bookmarks