Error-Search Operating Mode - Siemens SIMATIC S7-400H Manual

4.3.6

ERROR-SEARCH Operating mode

During the self-test the master CPU and the standby CPU compare the contents of
their memories. If the test discovers different memory contents, a comparison error
is reported.
The preset reaction to a comparison error is the ERROR-SEARCH mode (default
reaction). The purpose of the search for errors is to detect and localize a faulty
CPU.
You can modify the error reaction to a comparison error by means of configuration
– for example, the standby CPU is required to go to STOP instead of
ERROR-SEARCH in the event of a comparison error.
Error search sequence in Solo mode
System quits the Redundant system mode and goes to Solo mode.
Master CPU remains at RUN
Standby CPU goes to ERROR-SEARCH. Communications are not
possible.
Standby CPU goes to Defective
mode.
Master CPU continues to operate
at RUN.
Figure 4-3
If the self-test discovers a comparison error, the S7-400H quits the Redundant
system mode and the standby CPU continues working in ERROR SEARCH mode.
During the search for errors the standby CPU executes the entire self-test; the
master CPU remains at RUN.
S7-400H Programmable Controller Fault-Tolerant Systems
A5E00068197-04
Self-test detects different memory contents in the two CPUs
(comparison error)
Standby CPU executes complete self-test.
Error detected?
Error Search Sequence
System and Operating Modes of the S7-400H
No error detected?
Standby CPU links up again and
updates.
Operating system performs
master/standby switch.
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