Siemens SIMATIC S7 F Manual page 212

Fail-Safe Blocks
Error Handling
The F module drivers can detect errors as well as respond to errors reported by the
module. Each block has several options for signaling and handling errors.
F Channel Drivers
Installation in Cyclic Interrupt OBs
Every F channel driver block must be installed in a cyclic interrupt OB3x. Multiple
installation of an instance in different cyclic interrupts is not permissible. The cyclic
interrupt interval must be coordinated with the monitoring time configured for the
module in HWCONFIG.
When the Safety Program is compiled, a check is carried out to establish whether
an F channel driver has been installed in more than one cyclic interrupt OB. If
appropriate, a corresponding error message is output.
All the F channel drivers that belong to a module must be integrated into the same
F-run-time group.
Startup Characteristics
After a startup (cold restart or warm restart), communication must first be
established between the F module driver and the F-I/O. Until this happens,
substitute values are output with the quality code (QUALITY) 16#48 and the
outputs QBAD and PASS_OUT of the F channel drivers are set.
As soon as PROFIsafe communication has been established without any errors
and no more module or communication faults/errors occur, valid process values
are output.
If PROFIsafe communication cannot be established within the configured
monitoring time, a TIMEOUT error is detected.
See Also
"Error Handling of Driver Blocks"
Passivation and Reintegration
8-24
Fail-Safe Systems
A5E00085588-03