Technical data

S7 Communication
System Software for S7-300/400 System and Standard Functions - Volume 2/2
21-6 A5E00739858-01
Warm Restart and Cold Restart with SFBs for Unilateral Data Exchange
It is assumed that the server on the communication partner is operational after the
connections have been established, in other words that it can process jobs or
output messages at any time.
SFBs that send out jobs and expect acknowledgements react to a complete restart
as follows:
The current processing is aborted and the CFB branches to the NO_INIT status
immediately afterwards. If an acknowledgement for the job sent prior to the warm
or cold restart arrives later, it is discarded locally.
A new job may have been sent before the acknowledgement of the earlier job is
received.
SFBs that output or receive messages react as follows:
• The current processing is aborted and the CFB branches to the NO_INIT status
immediately afterwards.
• With SFB USTATUS, messages that arrive during the NO_INIT and DISABLED
statuses are discarded locally.
Reaction to a Hot Restart
The SFBs for S7 communication are set to the NO_INIT status only during a warm
or cold restart. This means that they react like user function blocks that can be
resumed following a hot restart.
Reaction to a Memory Reset
A memory reset always causes all connections to be terminated. Since a warm or
cold restart is the only possible startup type for the user program after a memory
reset, all SFBs for S7 communications (if they still exist) are set to the NO_INIT
status and initialized. Partner blocks in a module whose memory was not reset
change to the IDLE, ENABLED or DISABLED statuses as a reaction to the
connection being terminated.