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Rockwell Automation 1785-L20C_L40C, D17856.5.14 ControlNet PLC-5 Programmable Controllers User Manual User Manual

Page 31

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Chapter 2

Planning to Use Your ControlNet

PLCĆ5 Processor

2-3

Unscheduled DataĆTransfer Operations on a ControlNet Network

The ControlNet network allows you to use unscheduled messaging when
deterministic delivery is not required. Unscheduled operations include:

unscheduled non-discrete I/O data transfers—through ControlNet I/O

Transfer (CIO) instructions

peer-to-peer messaging—through Message (MSG) instructions

messaging from programming devices

The ControlNet system places your scheduled transfers in the first part
of each Network Update Interval (NUI), time is automatically reserved
for network maintenance, and unscheduled transfers are performed during
the time remaining in the interval.

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You reserve a

specific amount

of time for all

scheduled

operations

Any time remaining is used

for unscheduled operations

The system

reserves time

for network

maintenance

One occurrence of the NUT is a NUI

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Unscheduled messaging on a ControlNet network is non-deterministic.
Your application and your configuration—number of nodes, application
program, NUT, etc.—help determine how much time there is for
unscheduled messaging.

Important: The ControlNet network reserves time for at least one
unscheduled transfer per NUI.