Lenze DDS v2.3 - Manual (Page 172)

Drive PLC Developer Studio
Editors
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DDS EN 2.3
7.7.10 Feedbacks
Contrary to the standard function block diagram editor, the CFC editor can display feedbacks
directly.
Note that an internal intermediate variable will be generally created for the output of a box.
•
With operators the data type of the intermediate variable depends on the highest-order data
type of the inputs.
•
With constants the data type depends on the lowest possible data type, i.e. data type SINT
is assumed for constant ’1’.
If an addition is carried out with feedback and constant ’1’, the first input returns data type SINT,
whereas the second input remains undefined as a consequence of the feedback. Thus also the
intermediate variable is SINT-type. Only then will the value of the intermediate variable be
assigned to the output variable.
The illustration below shows an addition with feedback and an addition directly with a variable.
Variables x and y are to be INT-type in this case:
Addition with feedback: Addition directly with a variable:
The two additions differ as follows:
•
Variable y can be initialized with a nonzero value, whereas the intermediate variable of an
addition with feedback needs a zero.
•
The intermediate variable of the addition with feedback is SINT-type, that of the addition
with variable y of INT-type.
•
Variables x and y have different values from call 128. Although INT-type, variable x is
assigned value –128 as the intermediate variable has overflown. Variable y is assigned value
128.
7.7.11 Processing sequence
The CFC editor assigns a processing number to boxes, outputs, jumps, returns and labels and
processes the individual elements in this sequence at runtime.
•
On element insertion, this number will be automatically assigned in a topological sequence
(from left to right and from top to bottom).
•
If the sequence has already been changed, the new element will be assigned the number of
its topological descendant, and all higher numbers will be increased by one.
•
Moving an element will not affect the number.
•
The sequence influences the result and must therefore be changed under certain
circumstances.
•
If sequence display is activated, the element’s processing number is displayed in a grey field
in the top right-hand corner.
Processing sequence display on: Processing sequence display off:
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