Mitsubishi Electric MELSEC-Q-MR-JE-C Reference Manual page 20

When the library has been installed normally, the following message appears and the library appears on the tree.
3.
Expand the "FB/FUN" tree under "User Library", and add an FB to the program by dragging and dropping it.
Add the I/O label definition. If necessary, add the conditions such as the interlock or others.
2 FUNCTION DESCRIPTION
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2.4 How to Use FB Library