Appendix C: Network variables
Network variable are variables which can be exchanged cyclic between PC/CX1000. Any elementary or complex datatypes can be exchanged. A Publisher/Subscriber model is used. For deterministic communication the Realtime-Ethernet Driver for TwinCAT has to be installed.
Publisher/Subscriber Model
With the Publisher/Subscriber model one publisher makes variable available in the network. Any PC/CX1000 can 'subscribe' to one of these variables. The publisher can allow access for one PC/CX1000, a set of PC/CX1000 or all PC/CX1000 in the network. With a Broadcast the variable can be accessed from all PC/CX1000, a Multicast allows access to a set of selected PC/CX1000 and a Unicast allows access only to one PC/CX1000. A Subscriber can also be a Publisher. With this a bidirectional connection is possible.
Unicast
The Publisher allows access of a network variable only for one selected PC.
Multicast
The Publisher allows access of a network variable to a set of selected PCs.
Broadcast
The Publisher allows access of a network variable to all PCs in the network.