Siemens SIMATIC S7-300 Hardware And Installation Manual page 240

Glossary
Ground (to)
To ground means to connect an electrically conducting component to the
grounding electrode (one or more conducting components which have a very good
contact with the earth) across a grounding system.
Floating potential
Having no electrical connection to ground
Substitute Value
Substitute values are configurable values which output modules transfer to the
process when the CPU switches to STOP mode.
In the event of an input access error, a substitute value can be written to the
accumulator instead of the input value which could not be read (SFC 44).
Product version
The product version differentiates between products which have the same order
number. The product version is increased with each upwardly compatible function
extension, production-related modification (use of new components) or bug-fix.
FB
--> Function Block
FC
--> Function
Error Display
One of the possible responses of the operating system to a --> runtime error is to
display the error. The other possible responses are: --> error response in the user
program, CPU STOP.
Error handling via OB
When the operating system detects a specific error (e.g. access error with
STEP 7), it calls a dedicated organization block (Error OB) that determines
subsequent CPU response.
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S7-300 Programmable Controller Hardware and Installation
A5E00105492-02