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 module’s embedded 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 %MW words (4x registers) or unlocated variables for Global Data exchanges.
Key Features of Global Data
The main features for Global Data are:
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One publisher and multiple subscribers
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A device can publish one network variable of up to 512 %MW words (4x registers) or unlocated variables
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A device can subscribe to several network variables of up to 2048 %MW words (4x registers) or unlocated variables
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A device subscribes to the complete network variable
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One distribution group per network IP address
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Application defined publication rate
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Up to 64 Global Data network variables (numbered from 1 to 64) can be part of the data distribution group
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The NOE module has only one multicast address; consequently, it can only publish and subscribe inside the group
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A device can participate in several distribution groups by using multiple NOE communication modules 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:
