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model 3000 DeviceNet Module Manual (DN311/DN311A)
Chapter 1 Overview of the Devicenet Module
1
(c) Figure 1-7 shows the maximum distance between two nodes in cases where the
trunk line consists of thick and thin Cables with drop lines. Use the formulas in
Table 1-3 for calculating maximum cable lengths.
Maximum trunk line length between two nodes = Maximum cable length (value in
Table 1-3) minus the total length of drop lines for the nodes at both ends of the
trunk line.
In the case of Figure 1-7, the maximum trunk line length between node 0 and
node n will be equal to the maximum cable length (value in Table 1-3) minus the
drop line length between node 0 and node n.
Figure 1-7 Distance between Two Nodes on a Network with Drop Lines
L-thin: Length of trunk line using thin cable (m)
L-thick: Length of trunk line using thick cable (m)
1.2.3 Terminator
The DeviceNet needs a terminal resistor at both ends of a trunk line in order to reduce
signal reflections and stabilize communications. The specifications of the terminator are
as follows:
• 121Ω
• 1% of metal film
• 1/4 W
Terminators conforming with the above specifications are now commercially available.
See 3.6 Network Components.
Table 1-3 Maximum Cable Length (Mixed Use of Thick and Thin Cables)
Communication Rate Calculation Formula
125kbps
L-thick
+
5 × L-thin <= 500m
250kbps L-thick + 2.5 × L-thin <= 250m
500kbps L-thick + L-thin <= 100m
Node 0 Node 3
Node n
Te r m i n a t o r Te r m i n a t o r
Distance between two nodes <= Maximum cable length
L-thin L-thick
Usage Recommendations
• Make sure that your network configuration does not consist simply of extended trunk and
drop cables without nodes connected.
• Don't attach terminators to the nodes. It could cause communication errors.
• Don't attach a terminator to the ends of drop lines. Attach a terminator to both ends of
the trunk line;
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