Siemens S7-300 - Fault Reactions in Safety Mode with Parameter Setting Keep Last Valid Value

Fault reaction and diagnostics
6.1 Fault reactions of the F-SMs
Fail-safe signal modules
Installation and Operating Manual, 01/2010, A5E00085586-10
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6.1.3 Fault reactions in safety mode with parameter setting "Keep last valid value"
Applications
Typical applications for safety mode with parameter setting "Keep last valid value" are:
● Ventilation systems
● Smoke flaps
Fault reactions
Note
Consult the respective standards for installation.
NOTICE
Only standards EN54-2 /-4 or NFPA72 will be met with parameter setting "Keep last valid
value".
The last valid value will be retained in case of the following communication
errors/interruptions:
 STOP of F-CPU (interruption of PROFIsafe communication)
 Interruption of PROFIsafe communication
– in case of CRC errors
– Interruption of PROFIBUS/PROFINET connection
– Timeout of data frame monitoring
 Error in safety program of the F-CPU
 Error in PROFIsafe protocol
The current process value will be issued again once PROFIsafe communication resumes.
The safe status "0" will be assumed at the digital output module in case of the following
errors:
 Channel errors (independent of parameter "Behavior after channel faults")
 Module faults
With a pending channel fault in connection with
S7 Distributed Safety , the last valid value of
all error-free channels will be retained after a STOP-RUN transition of the F-CPU until
reintegration. You will have to correct the channel fault before reintegration if the parameter
"Behavior after channel fault" is set to "Passivate the entire module".
To increase availability use application 6 of the SM 326; F-DO 10 x DC 24V/2A PP.