User manual

Ethernet Communication Services
33002479 06 07/2008 89
Global Data
Overview The Global Data service is a real-time publisher/subscriber mechanism providing
the most efficient data exchange for PLC application coordination.
Devices that support 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 Global Data Configuration Page (see Configuration
of Global Data (Publish/Subscribe) by the Web for NOE 771 x1, p. 195) 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 %MW words (4x registers) for Global Data
exchanges.
Key Features of
Global Data
The main features for Global Data are:
z One publisher and multiple subscribers
z A device can publish one network variable of up to 512 %MW words (4x registers)
z A device can subscribe to several network variables of up to 2048 %MW words
(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's publish/subscribe mechanism allows multiple subscribers to receive a
single data transmission. This is an advantage over client/server services, which
require multiple transmissions to specific destinations. There are two immediate
benefits:
z reduces overall network traffic
z ensures tighter synchronization of multiple subscribers