Configuration planning – FANUC Robotics America GFK-1541B User Manual
Page 155
ries 90™ PLC User's Manual
–
May 2002
GFK-1541B
5
Configuration Planning
Producer and Consumer Periods for PLCs
Follow these guidelines for the producer and consumer periods.
Set the producer period and the consumer period to the same value. This makes the
system easier to troubleshoot and makes network resource usage more efficient.
Do not produce and consume data faster than is required by your application. This
reduces the load on the network and on the devices, providing capacity for other transfers.
For example, an exchange intended for an HMI host usually does not need to be produced
any faster than 500 milliseconds or so. In fact, a 1 to 3 second producer period may be
sufficient for this case.
Exchange Limitations and Recommendations
The limitations and recommendations for consumer and producer exchanges are as follows:
Maximum Number of Exchanges
The maximum number of exchanges can be divided up into any combination of producer and
consumer exchanges.
For a single Series 90-70 PLC system, which may contain multiple Ethernet Interfaces, the
maximum combined number of exchanges that can be configured is 255.
For the Series 90-30 CPU364 and the Series 90-30 CPU374, the maximum number of
exchanges that can be configured is 128.
Maximum Data Size of an Exchange
The total data size of a single exchange cannot exceed 1400 bytes. The total size is defined to be
the sum of the data lengths of all of the variables within the list.
Number of Variables
Up to 100 variables can be configured per exchange.
The minimum is one variable per exchange.
Different exchanges may have different variables, and they may share some or all of the same
variables even if the exchanges are produced and/or consumed at different rates.
It is possible to configure more EGD than a PLC can transfer either due to processing limitations
in the Ethernet Interface or in the underlying network (especially in 10Mbit networks). If you
configure too much EGD, you will experience high levels of consumer timeouts in some or all of
your consumed exchanges. In this case, you must reduce the EGD load. Possible approaches to
reducing the load include:
Increase the production period (especially if the period is more frequent than 2x the minimum
time in which the data is needed).
Redefine the exchanges to use fewer exchanges, each with more data. This can often be
achieved by making use of EGD groups (rather than producing a directed exchange to several
destinations, a single exchange produced to the group can contain all the data and each
consumer can transfer the data of interest from the exchange).
For Series 90-70 PLCs, consider adding an addition Ethernet Interface to the rack and
spreading the EGD exchanges.
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