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Rules for Failsafe Operation of an S5-95F
18.15 Loadable Function Blocks
Frequently repeated or particularly complex program sections (such as event signalling functions and
compute functions) are programmed in function blocks. These blocks have specifiable parameters
and an extended operation set (e.g. Jump operations within a block).
The loadable function blocks are subdivided into
•
User-written function blocks
•
Standard function blocks
User-Written Function Blocks
As is the case for all other blocks, function blocks written by the user must be examined by the
authorized inspector.
At the very least, such an examination comprises a verbal description of the function, functional
tests with attention to possible error conditions and a code analysis.
Standard Function Blocks
In the S5-95F, standard function blocks may be used only when they have been prototype-tested.
The standard FBs for the S5-95F implement the same functions as the standard FBs for the
SIMATIC S5 U-range controllers, but have been adapted to state-of-the-art failsafe technology. An
overview of the standard function blocks available for the S5-95F can be found in Catalog ST 57.
There are reaction-free and failsafe standard FBs. Only failsafe standard FBs may be used to form
signals relevant to the system's failsafety. When initializing the block parameters, note that output
parameters are failsafe only when all input parameters are failsafe.
All standard FBs are identified by a library number which, in conjunction with other measures,
protect the blocks against falsifications caused by transfer errors or disk errors.
Note the following when using loadable standard FBs:
•
In the safety mode, the operating system checks all standard FBs for integrity
•
Standard FBs for the SIMATIC S5 U-range controllers are not allowed, and are rejected in the
safety mode
•
The authorized inspector's examination of the standard FBs limits itself to
- a comparison of the library number with the one specified in the report
- checking for proper use of the standard FBs
- checking the FB calls for correctness and checking the parameter initialization routine for the
FBs as per the block description
- making sure that the provisions laid down in the report have been upheld
- checking the identity of the FBs with the aid of the entry in system event data block DB254
Note
When using standard FBs, flag words FW 200 to FW 254 may be used in the application
program only when these flags are saved prior to invoking a standard FB and reloaded
once that FB has executed.
18-32
S5-95F
EWA 4NEB 812 6210-02
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