Siemens SIMATIC S7-400H - The Operating States of the Cpus; Figure 11-2 System and Operating States of the Fault-Tolerant System

System and operating states of the S7–400H
11.3 The operating states of the CPUs
S7-400H
130 System Manual, 03/2012, A5E00267695-11
11.3 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 the startup, test, and error
diagnostics.
Operating states from POWER ON to redundant system state
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
redundant system state. The HOLD HOLD mode (Page 135) and ERROR-SEARCH
ERROR-SEARCH mode (Page 135) states are a special featu
re and are not shown.
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Figure 11-2 System and operating states of the fault-tolerant system