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(3) The Maximum Cable Length
The distance between two nodes on the network cannot exceed the "Maximum cable length"
specified in the DeviceNet specification. In Figure 1.4, the distance from node 0 to node 60 is not
allowed to exceed the "Maximum cable length."
The "Maximum cable length" varies depending on the communication rate of the
network and the type of the cable used for the trunk line.
a) Table 1.2 lists the maximum cable length for the case that the trunk line consists of a Thick
Cable alone and no drop line is connected on it (that is, all nodes are connected on the trunk line),
as shown in Figure 1.5. In this case, "maximum trunk line length between node 0 and node n" =
"maximum cable length."
Moreover, when the "maximum trunk line length between node 0 and node n" = "maximum
cable length," no new node can be attached outside node 0 and node n..
Node nNode 3Node 2Node 0
•
•
•
•
•
•
•
•
•
Distance between two nodes
≤
Maximum cable length
Terminal
resistor
Terminal
resistor
Figure 1.5 Distance Between Two Nodes on a Network With No Drop Line
Table 1.2 Maximum Cable Length (Thick Cable/Thin Cable alone)
Communication
Rate
Thick Cable
alone
Thin Cable alone
125 kbps 500 m 100 m
250 kbps 250 m 100 m
500 kbps 100 m 100 m
b) Figure 1.6 shows the maximum distance between two nodes in the case that a Thick Cable
or Thin Cable alone is used for the trunk line and that drop lines are used.
Table 1.2. lists the maximum cable length. In this case, the "maximum trunk line length
between two nodes" is as follows:
Maximum trunk line length between two nodes
= Maximum cable length
(value in Table 1.2)
− Total length of drop lines for both ends nodes of trunk line
For Figure 1.6, the maximum trunk line length between node 0 and node n is equal to the
maximum cable length (value in Table 1.2) minus total length of drop lines for node 0 and
node n.
Node n
Node 3Node 2
Node 0
•
•
•
•
•
•
•
•
•
Distance between two nodes
≤
Maximum cable length
Terminal
resistor
Terminal
resistor