Configuration
4.4 Basic communication mechanisms
CP 1243-8 IRC
Operating Instructions, 02/2018, C79000-G8976-C385-03
65
With the ST7 protocol which partner establishes a connection depends on the network type
and the configuration:
●
In communication via a dedicated line, the connection is always instigated by the
communications partner (polling).
●
Ethernet, Dial-up network, mobile wireless network, private wireless network
In communication via dial-up networks and IP-based communication, connections are
established by the CP as the client (spontaneous mode).
If a connection established by the CP is interrupted, the CP automatically attempts to re-
establish the connection.
Note
Connection interrupted by the mobile wireless network provider
When using mobile wireless services, remember that e
xisting connections can be
interrupted by mobile wireless network providers for maintenance purposes.
Connection establishment in Open User Communication and PG/OP communication
In Open User Communication in an S7 station, the CPU is the connection partner.
Connections are established as soon as the corresponding program blocks are called on the
CPU.
This also applies to the situation when a different S7 station sends data. In this case, the
corresponding receive blocks are called by the receiving station.
Acknowledgment
Acknowledgment of frames
The receipt of a sent frame is monitored and acknowledged in different ways. The
mechanisms differ depending on the type of communication and the telecontrol protocol:
Telecontrol communication
●
Frames sent by the master station are acknowledged immediately by the CP when
received.
Frames sent by the CP are acknowledged by the master station.
– Inter-station communication between stations
Received frames are acknowledged immediately by the CP. The acknowledgement
frame is forwarded by the master station to the sending CP.
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