The Operating States Of The Cpus; Figure 8-2 System And Operating Modes Of The Fault-Tolerant System - Siemens SIMATIC S7-400H System Manual

8.4

The operating states of the CPUs

Operating states describe the behavior of the CPUs at any given point in time. Knowledge of
the operating states of the CPUs is useful for programming startup, the test, and the error
diagnostics.
Operating states from POWER ON to system redundancy
Generally speaking, the two CPUs enjoy equal rights so that either can be the master or the
standby CPU. For reasons of legibility, the illustration presumes that the master CPU (CPU 0)
is started up before the standby CPU (CPU 1) is switched on.
The following figure shows the operating states of the two CPUs, from POWER ON to system
redundancy mode. The HOLD HOLD operating state (Page 87) and TROUBLESHOOTING
TROUBLESHOOTING operating state (Page 87) modes are special modes and are not shown.
Figure 8-2 System and operating modes of the fault-tolerant system
S7-400H
System Manual, 09/2007, A5E00267695-03
System and operating states of the S7-400H
8.4 The operating states of the CPUs
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