GE PACSystems RX7i, User Manual

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Chapter 5. Ethernet Global Data
GFK-2224Q January 2017 71
5.2 EGD Exchanges
Each exchange in EGD is identified by its Producer ID and Exchange ID. Up to 255 exchanges can be
configured for a PACSystems Ethernet Interface. They can be divided into any combination of produced and
consumed exchanges. Each exchange can be up to 1400 bytes in length.
Different produced exchanges can include some or all of the same data even though the exchanges are
produced at different rates and sent to different consumers. Consumed Exchanges should not duplicate where
the data is put as variable conflicts will occur and data will be overwritten by the multiple exchanges
Caution
Ethernet Global Data is designed for simple, efficient communication of sampled
data between devices. It is not intended for event notification where the
possible loss of a sample of data would be significant.
Some EGD devices support the concept of an EGD “page”. An EGD page consists of one or more exchanges that
are produced on the same schedule to the same destination. Pages remove the 1400 byte size limitation of
EGD exchanges. Machine Edition does not currently show information about EGD pages; you will instead see
the constituent exchanges for each page.
Content of an Ethernet Global Data Exchange
Each Ethernet Global Data exchange is composed of one or more data ranges transmitted as a sequence of 1
to 1400 bytes of data. The data ranges are commonly called variables; they may be configured to correspond
to PLC variables. The content of the data is defined for both the producer and consumers of the data. In this
example, a producer sends an 11-byte exchange consisting of the current contents of %R00100 through
%R00104 followed by the current contents of %I00257 through %I00264:
Address Length Type Description
%R00100 5 WORD Conveyor1 in PLC1
%I00257 1 BYTE Conveyor1 limit switch in PLC1
The same exchange can be configured at each consumer to suit the needs of the application.
Data Ranges (Variables) in an Ethernet Global Data Exchange
The variables within an exchange are defined in the Ethernet Global Data configuration in hardware
configuration. There can be:
▪
A length of 1 byte to 1400 bytes per exchange. The total size of an exchange is the sum of the data lengths
of all of the data ranges configured for that exchange.
▪
A maximum of 30,000 data ranges for all exchanges in the target, for CPUs with firmware version 5.0 or
later. (Earlier firmware versions allow approximately 12,000 EGD data ranges per target.)
Different produced exchanges may share some or all of the same data ranges even if the exchanges are
produced at different rates. A consumer does not have to consume all of the data from a produced exchange.
A consumed exchange may be configured to ignore specified data ranges. (See “Selective Consumption” in
Chapter 4.)