Special Features In Link-Up And Update Operations - Siemens SIMATIC S7-400H System Manual

9.5

Special features in link-up and update operations

Requirement for input signals during the update
Any process signals read previously are retained and not included in the update. The CPU
only recognizes changes of process signals during the update if the changed state remains
after the update is completed.
The CPU does not detect pulse signals (signal transitions "0 → 1 → 0" or "1 → 0 →1") which
are generated during the update.
You should therefore ensure that the interval between two signal transitions (pulse period) is
always greater than the required update period.
Communication links and functions
Connections on the master CPU are not be shut down. However, the CPU does not execute
any associated communication requests until the update is completed. They are queued for
execution as soon as one of the following cases occurs:
● the update is completed, and the system is in the redundant state.
● the update and master/standby changeover are completed, the system is in single mode.
● the update was aborted (due to timeout, for example), and the system has returned to
An initial call of communication blocks is not possible during the update.
CPU memory reset request on aborted link-up
If the link-up operation is aborted while the content of load memory is being copied from the
master to the standby CPU, the standby CPU requests a memory reset. This indicated in the
diagnostics buffer by event ID W#16#6523.
S7-400H
System Manual, 09/2007, A5E00267695-03
single mode.
9.5 Special features in link-up and update operations
Link-up and update
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