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08.89
2.2
Serial connection
In contrast to bus connection, with which all nodes are physically connected in parallel to a
common bus cable, every connection between two peers is implemented with a separate
connection cable in the case of serial connection.
Procedures agreed between the two nodes ensure the controlled data exchange between the
connected peers.
2.2.1
Point-to-point connection
The point-to-point connection ensures the communication between two peers. This is the
simplest form of process communication if it is established as direct connection (separate line)
between two nodes.
Complex communication relations can be logically traced back (to a large extent) to a
combination of these simplest relationships.
If exactly this case occurs in practice, even the simplest type of connection is adequate.
Process communication point-to-point connection
Station 1
•
Data transfer between two peers
•
Simplest case of process communication
•
Simplest type of connection is adequate (4-wire)
•
Example: PLC/PG traffic on SIMATIC systems
Exactly one physical point-to-point connection corresponds to each connection i.e. each
existing request of a unit to exchange data with a partner station.
Depending on the number of nodes involved, cabling expenditure is high and costs will
increase progressively if a further station is to be connected and wishes to communicate with
all other stations. Larger networks cannot be implemented due to the required number of
interfaces per unit increasing considerably.
Fault diagnosis is relatively simple since an unambiguous allocation is possible according to
communication request and physical implementation.
© Siemens AG 1989 All Rights Reserved
SINUMERIK 840/880 (PJ)
6FC5 197-0AB20-0BP0
2 Local Area Networks
2.2 Serial connection
Station 2
2–9
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