Safety in F-Systems
4.2 Safety Mode
Safety Engineering in SIMATIC S7
4-4
System Manual, 04/2006, A5E00109529-05
Monitoring Time and Sequence Number
The F-CPU assigns a sequence number to the F-I/O for time monitoring of the message
frame update in the PROFIsafe protocol.
A valid, current safety message frame with a valid sequence number must be received by
the F-CPU and the F-I/O within an assignable monitoring time.
If a valid sequence number is not detected within the monitoring time, the F-I/O is
passivated.
CRC (Cyclic Redundancy Check) Signature
A CRC signature contained in the safety message frame protects the validity of the process
data in the safety message frame, the accuracy of the assigned address references, and the
safety-relevant parameters.
If a CRC signature error occurs during communication between the F-CPU and F-I/O,
e.g., due to intermittent electromagnetic interference, the F-I/O is passivated.
See also
Introduction (Page 3-13)
Fault Reactions (Page 4-5)
Configuring the Monitoring Times (Page A-2)
