Siemens SIMATIC S7 F Manual page 292

Fail-Safe Blocks
I/Os
Name
Inputs:
CU
CD
R
LOAD
PV
Name
Outputs: QU
QD
CV
Note
If, when you create the program, you preset the CV output in CFC with an initial
value of < 0 or > 0, the counter is incremented or decremented as of this value.
Note that the initial values of output parameters do not appear in the printout of the
CFC chart. They must be checked in the printout of the safety program.
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.
Error Information in Diagnostic Buffer
Error Code (W#16#...)
75DAH
8-104
Data Type Explanation
F_BOOL Up-counting input
F_BOOL Down-counting input
F_BOOL Reset input (R dominates over
LOAD)
F_BOOL Load input (LOAD dominates
over CU and CD)
F_INT Preset value
Data Type Explanation
F_BOOL Status of the up counter
QU has the value
– 1 if CV >= PV
– 0, otherwise
F_BOOL Status of the down counter
QD has the value
– 1 if CV <= 0
– 0, otherwise
F_INT Current count value
Description
Error in the safety data format of the input CU, CD, R, LOAD
or PV (error due to online modification of the Safety Program
or internal CPU fault)
Default
0
0
0
0
0
Default
0
0
0
Fail-Safe Systems
A5E00085588-03