Siemens SIMATIC S7 F, Manual

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Fail-Safe Blocks
Fail-Safe Systems
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A5E00085588-03
8.6.1 F_CYC_CO
Function
This block monitors the cycle time of its priority class (cyclic interrupt OB 3x) and
provides a fail-safe time base for other F blocks.
At compilation, the block is inserted automatically into a F-run-time group named
@F_CycCo-OB3x, where x is 0 through 8 that correspond to the OB3x containing
F-Blocks, that contain the blocks F_TESTC and F_TEST.
If the value of MAX_CYC is invalid, a new value will be requested at compile time.
See "Configuring the Monitoring Times for F/FH Systems".
!
Safety Note – PD_FLAG not to be interconnected
The invisible output PD_FLAG must not be interconnected.
I/Os
Name Data Type Explanation Default
Inputs: MAX_CYC F_TIME Maximum permissible
F cycle time T# 0s
PD OFF F_BOOL Power Down Monitoring 0
Outputs: PD FLAG F_BOOL Power-off code 0
DIFF F_DINT Time difference since the last
cycle in ms 0
CYC_SQ F_INT Sequence number 0
FAILED BOOL Failure of the OB Indicator 0
Error Handling
In the event of an error that is critical to safety, the system function SFC F_CTRL
is called. This records the event in the Diagnostic Buffer and requests a switch to
the reserve CPU if the error occurred only on the master CPU. For non-redundant
systems or a common-cause error occurring in both CPUs, the shutdown logic can
be configured to either disable the erred F-run-time group or the entire Safety
Program.