<4. Control Application Creation>
In this segmentation, while the worksheet is organized by individual functions of
analog input, NPAS_PID and analog output, the connections between the
NPAS_POUs are not implemented by direct links, but implemented through data
passing by variables. As a result, the data flow and inter-block relationships are not
visually captured, which destroys one of the features of FBD. This counter example
shows how over segmentation can produce a more complicated application.
In short, code worksheet segmentation by function is necessary for creating simple
applications but over segmentation may actually increase complexity.
● Segmentation of Program POU
Besides code worksheet segmentation, program POU creation by function is also
allowed.
Analog input
NPAS_PID
Analog output
Program POU A
MV=0% sequence logic
Program POU B
Analog input
NPAS_PID
Analog output
MV=0% sequence logic
ＰＶ value calculation processing
Logic for writing ＳＶ value
Unsegmeted program POU
Logic for writing ＳＶ value
Program POU C
PV value calculation processing
Program POU D
However, doing this increases complexity as connections between program POUs
are implemented through global variables instead of local variables.
Therefore, unless there are special reasons such as the size of one program POU
exceeding the system limit, segmenting a program POU is not recommended.
If the data in the FCN-500 orFCN-RTU is referenced from the outside (e.g. via
FCN/FCJ OPC server), you need to pay attention to the length of a variable name
and a POU instance name..
- Variable name, instance name: up to 30 characters
The hierarchy of POU can be up to 6. If it is referred to as "POU instance
name .POU instance name .------. Variable name", it will be up to 216 characters.
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