Rockwell Automation 1786-series ControlNet Coax Media Planning and Installation Guide - Manual (Page 13)

Publication CNET-IN002B-EN-P - June 2010 13
ControlNet Cable System Overview Chapter 1
Trunk Line Terminating Resistors
A 75
Ω
terminating resistor
must be installed on the tap at each end of a
trunk-cable section. Terminating resistors absorb the electrical energy of the
signal at the ends of the cable to prevent reflections, which interfere with
signals that are being sent.
Two types of terminating resistors are available depending on the connectors
and taps that are being used on a trunk line. There is a BNC terminating
resistor (catalog number 1786-XT) and a TNC terminating resistor
(catalog number 1786-TNCLXT4).
Segment
A segment is a collection of coax trunk cable sections and taps, bounded by
terminating resistors at each end of the segment. The total allowable length of
a segment depends upon the number of devices attached to the segment via
the taps.
You cannot have more than 48 active devices and taps on a single coax
segment. A repeater (see
page 14 ) lets you extend the allowable cable distance
for additional nodes (maximum of 99 on a ControlNet network).
1786-TNCLXT4 1786-XT
Segment
TR TR
T T T T
N N N N
Trunk Line
Drop Line
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