Hardware reference guide

Ethernet Modules
35013379 11/2011 311
Global Data
Global Data service is a real time Publisher/Subscriber mechanism providing the
most efficient data exchange for PLC application coordination.
Devices supporting Global Data are arranged in a distribution group for the purpose
of application variable exchange and synchronization. Each Global Data device can
publish up to one network (application) variable and subscribe up to 64 network
(application) variables.
The Quantum NOE’s embedded Web Global Data Configuration Page provides a
configuration screen to determine which and how many application variables are
exchanged with this service. After configuration, the exchanges between all stations
belonging to the same distribution group are done automatically.
The Global Data service uses the 4x register space for Global Data exchanges.
Key Features of Global Data
The main features for Global Data are:
z One Publisher and many Subscribers
z A device can publish one network variable of up to 512 registers
z A device can subscribe to several network variables of up to 2048 4x registers
z A device subscribes to the complete network variable
z One distribution group per network IP address
z Application defined publication rate
z Up to 64 Global Data network variables (numbered from 1 to 64) can be part of
the data distribution group
z An NOE has only one multicast address; consequently, it can only publish and
subscribe inside the group
z A device can participate in several distribution groups by using multiple NOEs in
the rack
Global Data has an advantage over Client/Server services when more than one
Subscriber is receiving the same data since only one transaction is necessary for all
Subscribers to receive the data.
This advantage offers two benefits:
z Reduce overall network traffic
z Ensure tighter synchronization of multiple subscribers