IEC60870-5-102
TF6500 implements one interface for the transport of the IEC 60870-5-102 ASDUs (service data unitof the application layer) via the serial interfaces of the pc and the Beckhoff KL6xxx/EL6xxx bus terminals.
The end application is imposed on the software interface of the PLC library. Unlike the implementation of other 101/104 TwinCAT products only one "so called" 'Low level' interface is available. The reason: The IEC 60870-5-102 devices are featuring a lot of vendor specific data. The 'Low level' interface allows the access to this data. The characteristics of both interfaces are described briefly below.
'Low level' interface:
This interface starts lower down on the protocol stack and enables the sending and/or receipt of individual frames (ASDUs). This interface is placed inside the protocol structure above the link layer (2) and implements necessary transport functions and frame formats. Application functions like for example the general request or time synchronisation are not implemented in the interface, but the user can implement them by himself.
Pro: Very flexible; all properties in the ASDU frame can be changed (e.g. an own time stamp, Select/Execute or a special command execution etc.); high performance can be achieved because only the necessary services are implemented; high performance if there are many data points;
Contra: Larger amount of programming work; all services, such as general query, counter query, time synchronisation, command execution, spontaneous data transmission etc. must be implemented by the PLC programmer himself (programmed out); the PLC programmer must be familiar with the protocol standard.
Protocol structure of endsystem:
Protocol structure of the end system:
Selection of application functions from IEC 60870-5-5 | User process |
|---|---|
Selection of ASDU (service data units of the application layer) from IEC 60870-5-3, IEC 60870-5-4 and IEC 60870-5-102 | Application layer (7) |
N/A | Presentation layer (6) |
Session layer (5) | |
Transport layer (4) | |
Network layer (3) | |
unbalanced IEC 60870-5-2 IEC 60870-5-1 (FT 1.2) | Link layer (2) |
EIA RS485, RS232 (V.24), Fiber Optics | Physical layer (1) |
 | Layers 3 to 6 are not used. |