Siemens SIMATIC PCS 7 Configuration Manual page 114

Configuration of the hardware (AS and I/O)
6.5 Configuration of the I/O devices
Note
The following naming conventions apply to all components in HW Config:
The name should not exceed 14 characters. When generating the module drivers (CFC
compilation), the names from HW Config are used for the CFC block instances. CFC blocks
can have a maximum of 16 characters. The module driver wizard shortens the names from
HW Config to 14 characters and always adds "_1".
Make sure that the assigned names are unique. Simply changing the case of names does not
make them unique, as the OS compilation procedure does not take case into account.
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Compendium Part A - Configuration Guidelines (V8.2)
Configuration Manual, 08/2016, A5E38166869-AA