1.2 Programming the Safety Program
1.2.1 Differences between F-Programming Languages and Standard
Programming Languages
Access to Data Blocks
Data blocks should always be accessed with "fully qualified DB access" to ensure
that the correct data block is opened.
The initial access to data of a data block in an F-FB/F-FC must always be a "fully
qualified DB access," or it must be preceded by the "OPN DB" operation. This also
applies to the initial access to data of a data block after a jump label.
Options for the data blocks "Unlinked" and "DB is write-protected in the AS"
Note
The adjustable option "Unlinked" in the object properties of a DB must not be set
for the F-DBs and instance DBs of the F-blocks.
The selectable option "DB is write-protected in the AS" in the object properties of
the of a DB must not be set for F-DBs and instance DBs of F-blocks.
If you have set one of the options listed above, this is corrected when you compile
the safety program.
Boolean Constants "0" and "1"
If you require the Boolean constants "0" and "1" in your safety program to assign
values to parameters during block calls, you can use the tags "RLO0" and "RLO1"
in the F shared DB with full qualified DB access ("F_GLOBDB".RLO0 or
"F_GLOBDB".RLO1).
Product Information for the S7 Distributed Safety, Configuring and Programming Manual
28 A5E00169432-02
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