TcIEC870_5_104: IEC 60870-5-104 Transport Interface (master/slave

The library TcIEC870_5_104.Lib implements an interface. Via this interface single ASDUs ( service data unitof the application layer) can be sent and received. This interface is placed inside the protocol structure above the transport layer (4) and implements already the APCI functions (protocol control information of the application layer, see lower table ). Application functions like for example the general request and count request are not implemented in the interface, but the user can implement them by himself.

'Low level' interface: IEC 60870-5-104 Transport Interface

This interface starts lower down on the protocol stack and enables the sending and/or receipt of individual frames (ASDUs).

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.

This interface is recommended if you:

are familiar with the protocol standard;
are implementing a protocol converter application;
are implementing virtually all available standard functions in the application;
are using special functions, such as the relaying of the time stamp from a Modbus device or the gaining of control over the command execution;
require functions that are not supported according to the compatibility list;
have many data points (>1000) and need high performance;

Protocol structure of endsystem:

Requirements

Selection of application functions from IEC 60870-5-5 to IEC 60870-5-101	Initialisation	Application process
Selection of ASDU (service data unit of application layer) from IEC 60870-5-101 and IEC 60870-5-104		Application layer (7)
TwinCAT PLC Library: IEC 60870-5-104 (low level) Transport Interface
APCI (Protocol control information of the application layer) Transport Interface (user to TCP interface)
Selection of TCP/IP protocol collection (RFC 2200)		Transport layer (4)
		Relaying layer (3)
		Connection layer (2)
		Physical layer (1)

Remark: The layers 5 and 6 are not used.

Further Information