Siemens SIMATIC S7-400H - Operating Modes of the CPUs

System and Operating Modes of the S7-400H
5-5
Automation System S7-400H Fault-tolerant Systems
A5E00068197-07
5.3 Operating Modes of the CPUs
Operating modes describe the behavior of the CPUs at any given point of time.
Knowledge of the operating modes of the CPUs is useful for programming startup,
the test and the error diagnostics.
Operating modes from POWER ON to redundant system mode
Generally speaking, the two CPUs enjoy equal rights so that either CPU can be the
master or the standby CPU. For reasons of legibility, the illustration presupposes
that the master CPU (CPU 0) is energized prior to the standby CPU (CPU 1) being
energized.
Figure 5-2 deals with the operating modes of the two CPUs from POWER ON up
to redundant system mode. HOLD mode (refer to Section 5.3.5) and
ERROR-SEARCH (refer to Section 5.3.6) are not listed since they are a special
case.
Updating of dynamic
data
Updating the user
program
STOP
POWER ON at CPU 0
STARTUP
RUN
RUN
RUN
RUN
1.
2.
3.
4.
5.
6.
POWER ON at CPU 1
STARTUP/
LINK-UP
UPDATE
RUN
Stop
Startup
Single Mode
Linking
Update
Redundant mode
System mode
Master CPU
Standby CPU
STOP
STOP
STOP
Figure 5-2 System and operating modes of the fault-tolerant system