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c) Figure 1.7 shows the maximum distance between two nodes in the case that the trunk line
consists of Thick Cable and Thin Cables and that drop lines are connected. Use the formulas in
Table 1.3. for calculating the maximum cable length.
In this case, the "maximum trunk line length between two nodes" is represented in the
following formula:
Maximum trunk line length between two nodes
= Maximum cable length (value in Table 1.3)
− Total length of drop lines for the nodes at
both ends of trunk line
For Figure 1.7, the maximum trunk line length between node 0 and node n is equal to the
maximum cable length (value in Table 1.3) minus the total length of the drop lines for node 0 and
node n.
Node nNode 3Node 0
•
•
•
•
•
•
•
•
••
•
•
•
•
•
•
•
•
Distance between two nodes
≤
Maximum cable length
Terminal
resistor
Terminal
resistor
L-thin L-thick
Figure 1.7 Distance Between Two Nodes on a Network with Drop Lines
Table 1.3 Maximum Cable Length (Mixture of Thick Cable/Thin Cable)
Communication
Rate
Calculation Formula
125 kbps L-thick + 5 × L-thin ≤ 500 m
250 kbps L-thick + 2.5 × L-thin ≤ 250 m
500 kbps L-thick + L-thin ≤ 100 m
L
-
thin: Length of trunk line using thin cable (m)
L
-
thick: Length of trunk line using thick cable (m)
1.2.3 The Terminal Resistor
The DeviceNet needs a terminal resistor on both ends of the trunk line in order to reduce signal
reflections and stabilize communications. The specifications of the terminal resistor are as follows:
• 121Ω
• 1% of the metal film
• 1/4 W
Terminal resistors conforming with the above specifications are available in the commercial market.
See "3 .6 The Network Components."
Usage Recommendation
1. Don't make a network configuration whose extended trunk line and drop lines have no node
being connected.
2. Don't attach a terminal resistor to the node. It could cause communication error.
3. Attach a terminal resistor to both ends of the trunk line; don't attach a terminal resistor on the