Troubleshooting Operating State - Siemens SIMATIC S7-400H Manual

System and Operating Modes of the S7-400H
5.3.6

TROUBLESHOOTING Operating State

During the self-test, the master and standby CPUs are compared. If the test
discovers a difference, an error is reported. Possible errors are hardware faults,
checksum errors and RAM/PIQ comparison errors.
The following events will trigger TROUBLESHOOTING mode:
1. If, in redundant mode, there is a one-way call of OB 121 (only on one CPU), a
hardware fault is assumed and this CPU goes into TROUBLESHOOTING
mode. The other CPU becomes the master, if necessary, and continues in
single mode.
2. If, in redundant mode, a checksum error occurs on only one CPU, this CPU
goes into TROUBLESHOOTING mode. The other CPU becomes the master, if
necessary, and continues in single mode.
3. If, in redundant mode, a RAM/PIQ comparison error occurs, the standby CPU
goes into TROUBLESHOOTING mode (default reaction) and the master CPU
continues in single mode.
The response to a RAM/PIQ comparison error can be changed by means of
configuration (e.g. the standby CPU goes into STOP).
The purpose of TROUBLESHOOTING mode is to detect and localize a faulty
CPU. During the search for errors the standby CPU executes the entire self-test;
the master CPU remains in RUN mode.
If an error is detected, the CPU goes into DEFECTIVE mode. If no error is
detected, the CPU links up again. The fault-tolerant system goes into redundant
system mode again. An automatic master-reserve swtichover then takes place.
This ensures that when the next error is detected in TROUBLESHOOTING mode
the hardware of the previous master CPU is tested.
No communication is possible in TROUBLESHOOTING mode.
For further information on the self-test, see Section 5.4.
5-10
Automation System S7-400H Fault-tolerant Systems
A5E00068197-07