Allen-Bradley ControlNet Compact GuardLogix 1769, User Manual, Page: 16 / 100

Chapter 1 ControlNet Overview
Network Update Time (NUT)
The network update time (NUT) is the shortest interval in which data can be
sent on a ControlNet network. It represents the fastest possible update rate for
scheduled data transfers on that network. For example, a network that runs with a
five ms NUT cannot send scheduled data at a rate faster than five ms. It can,
however, send data at a slower rate. The minimum NUT you can specify is two
ms. The NUT is divided into a three-part structure.
Table 4 - NUT Structure
Parts of NUT Functions
Scheduled
On a sequential, rotating basis, every scheduled node can transmit data once per
NUT.
Time-critical information is sent during this part of the interval.
Unscheduled All nodes transmit on a sequential, rotating basis, the rotation repeating itself
until the time allotted for this portion is used up.
The number of scheduled transmissions determines the time available for
unscheduled transmissions. On a ControlNet network, at least one node can
transmit unscheduled data every NUT.
Information that can be delivered without time constraints is sent during this
part of the interval.
Maintenance The node with the lowest address transmits information to keep the other nodes
synchronized. This time is automatically subtracted from your NUT. However, the
time required for network maintenance is brief (microseconds) when compared
to that used for the scheduled and unscheduled portions of the NUT.
Figure 4 - NUT Structure
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3
Item Description
1 Boundary moves according to scheduled traffic load
2 Unscheduled traffic
3 Network maintenance
4 Scheduled traffic. Each device transmits only once
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16 Rockwell Automation Publication CNET- UM001E-EN-P - June 2016