Technical data

Table Of Contents
S7 Communication
System Software for S7-300/400 System and Standard Functions - Volume 2/2
A5E00739858-01
21-5
21.2 Startup Routine of SFBs for Configured S7
Connections
Requirements
In the following description for S7-400, it is assumed that:
The connection descriptions (SDBs) exist on the modules.
The configured connections have been established.
The actual parameter for the ID matches the configured connection ID for each
SFB.
Warm Restart and Cold Restart
During a warm and a cold restart all SFBs are set to the NO_INIT status. The
actual parameters stored in the instance DBs are not changed.
Warm Restart and Cold Restart with SFBs for Bilateral Data Exchange
In general, the two modules with SFBs for bilateral data exchange do not both go
through a warm or cold restart simultaneously. The reaction of the SFB is governed
by the rules below:
The receive blocks (SFBs URCV, BRCV) react as follows:
If the SFB has received a job but has not acknowledged this job at the time of
the warm or cold restart, it generates a sequence abort frame (CFB, BRCV) and
then immediately branches to the NO_INIT status.
With SFB BRCV, it is possible that another data segment will be received
despite having sent the sequence abort. This will be discarded locally.
SFB URCV changes to the NO_INIT status immediately.
The send blocks (SFBs USEND, BSEND) react as follows:
If SFB BSEND has started a job sequence that has not yet been completed, it
sends a sequence abort when the warm or cold restart is initiated. It then
branches to the NO_INIT status immediately afterwards. An acknowledgement
that arrives at a later time is discarded locally.
If SFB BSEND has already sent or received a sequence abort when the warm
or cold restart is requested, it changes immediately to the NO_INIT status.
In all other cases and whenever the SFB sends only messages (for example,
SFB USEND), local processing is aborted and the SFB immediately branches to
the NO_INIT status.