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

Link-up and update

12.5 Special features in link-up and update operations

12.5 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 signal state
remains after the update is completed.
The CPU does not detect pulses (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, associated communication
jobs are not executed during updates. 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/reserve changeover are completed, the system is in single mode.
● The update was canceled (e.g. due to timeout), and the system has returned to single
An initial call of communication blocks is not possible during the update.
Memory reset request on cancelation of link-up
If the link-up operation is canceled while the content of load memory is being copied from the
master to the reserve CPU, the reserve CPU requests a memory reset. This indicated in the
diagnostic buffer by event ID W#16#6523.
168
mode.
System Manual, 03/2012, A5E00267695-11
S7-400H