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PLC and HMI Development with Siemens TIA Portal
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Despite Siemens' excellent approach toward UDTs and structs, there are some drawbacks to using them.
Most of the issues are small and are easily managed, however, a potentially confusing issue (especially to programmers that are new to using libraries and UDTs) occurs when a UDT and a block dependent upon the UDT both appear in a Project library.
UDTs that are stored in a library and are utilized in many places can cause a large number of objects to upgrade to a newer version if modified.
Remember
A program block is dependent upon a UDT if its interface contains a declaration of the UDT.
When a project library has no objects in test, it would look something like the following:
Figure 3.20 – Project library containing UDTs and function blocks
If UDT_Sample_Pump_Raw_IO
is modified and a new version is created, the project library indicates that the UDT is in test:
Figure...
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