Siemens SIMATIC S7-400H - Operating States HOLD; When Is HOLD Mode Possible?

System and Operating Modes of the S7-400H
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Automation System S7-400H Fault-tolerant Systems
A5E00068197-07
5.3.5 Operating States HOLD
Except for the additions described below, the S7-400H behaves in exactly the
same way in HOLD mode as an S7-400 standard CPU.
HOLD mode is a special case. It is only used for test purposes.
When is HOLD mode possible?
HOLD mode can be reached only from STARTUP mode and from RUN submode
of single mode.
Characteristics
• While the fault-tolerant CPU is in HOLD mode, link-up and update are not
possible; the standby CPU remains in STOP mode with a diagnostics message.
• If the fault-tolerant system remains in redundant system mode, no hold
positions can be set.