Glossary

substation, slave, server, controlled station

Synonyms for a subordinate station (which is monitored)

central station, master, client, controlling station

Synonyms for a higher-level station (control station, monitors others stations)

control direction

Data transfer direction from the central station to the substation

monitoring direction

Data transfer direction from the substation to the central station

application objects

IEC information objects in the TwinCAT PLC application (single points, double points, measured values, short floating point values etc.)

APDU

Application protocol data unit

APCI

Application protocol control information

ASDU

Application service data unit

IOA, information object address

Address of the single point, double point, measured value, short floating point value etc.

primary station

Primary station sends commands/requests to the secondary station and controls the data transmission of the secondary station.

secondary station

Secondary station anwers to the requests of the primary station.

combined station

Combined stations are able to act as primary and secondary station (balanced mode).

balanced mode

In balanced mode both stations act as primary and secondary stations and are able to initialize the data transmission.

unbalanced mode

In unbalanced mode only the primary station is able to initialize the data transmissions.

The central station acts as primary station and the substation acts as secondary station.

CAA

Common ASDU address

COT

Cause of transfer