Rockwell Automation DeviceNet Media Design Installation Guide - Manual (Page 19)

Publication DNET-UM072C-EN-P - July 2004
Get Started 1-9
Determine the cumulative drop line length
The cumulative drop line length refers to the sum of all drop lines, thick or thin
cable, in the cable system. This sum cannot exceed the maximum cumulative
length allowed for the data rate used.
The following example uses four T-Port (single-port) taps and two DevicePort™
(multi-port) taps to attach 13 devices to the trunk line. The cumulative drop line
length is 42m (139 ft) and no single node is more than 6m (20 ft) from the trunk
line. This allows you to use a data rate of 250k
bit/s or 125k bit/s. A data rate of 500k bit/s cannot be used in this example
because the cumulative drop line length (42m) exceeds the total allowed (39m)
for that data rate.
The data rate you choose determines the trunk
line length and the cumulative length of the drop
line.
The maximum cable distance from any device
on a branching drop line to the trunk line is 6m
(20 ft).
Data rate Cumulative drop line length
125k bit/s 156m (512 ft)
250k bit/s 78m (256 ft)
500k bit/s 39m (128 ft)
TR TR
2m (6.6)
3m (10 ft)
5m
(16 ft)
4m
(13 ft)
4m (13 ft)
2m(6.6 ft)
4m (13 ft)
3m (10 ft)
3m (10 ft)
2m (6.6 ft)
3m (10 ft)
2m (6.6 ft)
3m (10 ft)
DevicePort tap
(4 ports)
DevicePort tap
(8 ports)
= trunk line
= drop line
= device or node
TR = terminating resistor
1m
(3.3 ft)
1m
(3.3 ft)
41853