Configuring Fail-Safe As-As Communication - Siemens SIMATIC PCS 7 Operating Manual

You can use the F_LIM_R F block to check the result of a floating-point operation for
overflow (± infinite) and invalid floating-point number (NaN).
● A limit violation is indicated by IN > MAX or "+ infinite". MAX is output at OUT. OUTU is
set to 1 and OUTL to 0.
● A limit violation is indicated by IN < MIN or "- infinite". MIN is output at OUT. OUTU is set
to 0 and OUTL to 1.
● If IN is between MIN and MAX, the input IN is forwarded to the output OUT. OUTU and
OUTL are set to 0.
● If IN is an invalid floating-point number (NaN), the substitute value SUBS_IN is output at
OUT. OUTU and OUTL are set to 1.
Note
You can find a detailed description of the F blocks in the help for the blocks, as well as in the
"S7 F/FH Systems – Configuring and Programming"
(https://support.industry.siemens.com/cs/ww/en/view/101509838) manual.
7.3

Configuring fail-safe AS-AS communication

Like standard communication, safety-related communication between the safety programs of
F CPUs via S7 connections is implemented using connection tables in NetPro.
In S7 F/FH systems, safety-related communication via S7 connections is possible between
all 41x-xH CPUs.
In the case of F Systems V6.0 with S7 F Systems Lib V1_3 and higher, fail-safe
communication to S7 Distributed Safety is also supported with the following F CPUs:
● CPU 416F
● CPU 31xF
Note
Safety-related AS-AS communication is not permitted via public networks.
Compendium Part B - Process Safety (V8.2)
Operating Manual, 07/2016, A5E35031794-AB
Configuring the safety program
7.3 Configuring fail-safe AS-AS communication
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