<8. Detailed Description>
8.4.2 Selecting between FBD and LD
In Logic Designer, one logical POU is generally created using one language.
FBD and LD, however, are the exceptions and can be easily combined in the code.
For instance, an application can be coded in LD on an FBD logical POU, or coded in
FBD on an LD logical POU. As described in Section 8.4.1, “Selection Criteria for
FBD, LD and ST,” both FBD and LD are suitable for programming regulatory control
of analog signals, and have similar application representation and coding method.
Thus, there is no need to differentiate strictly between FBD and LD. Engineering
can begin with either FBD or LD, and if required, the application can be
subsequently coded with the other language that was not selected initially.
If both FBD and LD are used on the same code worksheet, the criterion for deciding
the execution sequence of the control application part coded in FBD changes.
When coding FBD and LD on the same code sheet, always verify the execution
order. For details, see Section 9.1.4, “Execution Order of Control Application” of
Chapter 9, “Advanced Engineering.”
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