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Table Of Contents
S7 Communication
System Software for S7-300/400 System and Standard Functions - Volume 2/2
A5E00739858-01
21-7
21.3 How SFBs React to Problems
The following section describes how SFBs for S7 communication in S7-400 react to
problems.
Connection Terminated
The connections allocated to the SFB instances are monitored.
If a connection is terminated, the reaction of the SFB depends on its internal status.
If the break down of the connection is detected while the block is in the IDLE or
ENABLED status, the SFB reacts as follows:
• It branches to the ERROR status and outputs the error ID "Communication
problems" at the ERROR and STATUS output parameters.
• When it is next called, the block returns to its original status and checks the
connection again.
A communication SFB that is not in the IDLE or DISABLED statuses reacts as
follows:
• It aborts processing, changes to the ERROR status immediately or at the next
block call and outputs the error ID "Communication problems" at the ERROR
and STATUS output parameters.
• When it is next called, the block changes to the IDLE, DISABLED or ENABLED
status. In the IDLE and ENABLED status the connection is checked again.
This procedure will also be executed if the connection has again been set up in the
meantime.
Power Down
A power down with battery backup followed by a restart causes all established
connections to be terminated. The points made above therefore apply to all blocks
involved.
If there is a power down with battery backup followed by an automatic warm or cold
restart, the points made about terminated connections and warm or cold restarts
apply.
In the special case of an automatic warm or cold restart without battery backup,
where a memory reset is executed automatically after power returns, the SFBs for
S7 communications react as described in the section "Startup Routine of the SFBs
For S7 Communications."
Reaction to Operating Mode Changes
If the operating mode changes between the STOP, START, RUN, and HOLD
statuses, the communication SFB remains in its current status (exception: during a
warm or cold restart, it changes to the NO_INIT status). This applies both to SFBs
for unilateral as well as SFBs for bilateral communication.