Chapter 3 System Configuration
3-4
3.2.2
Restrictions on Connection Configuration
1] Restrictions on maximum network length
The maximum network length refers to the distance between the devices that are farthest apart or the
longest of the trunk line distances (between termination resistors).
The communication cables in the network can be either of the two types: thick cable (trunk cable) or thin
cable (drop cable).
There is only a slight signal damping in a thick cable, thus it can be used for communication over
relatively long distances.
On the other hand, the signals tend to be attenuated in a thin cable; this type of cable is thus not suited
for communication over long distances.
The following tables list each cable specification and the restriction values corresponding to the
communication speeds.
Refer to the page 3-4 and 3-5 for definition of drop line length , total drop line length.
Table 3.2 Cable specification
Thick cable
Thin cable
Recommended
manufacturer
Showa Electric Wire &
Cable Co., Ltd.
Recommended
manufacturer
Showa Electric Wire &
Cable Co., Ltd.
Type TDN18
Type TDN24
Configuration Signal
pair Power supply
pair
Configuration Signal
pair Power
supply pair
Size (AWG)
18
14
Size (AWG)
24
22
Specifi
cation
Standard outer
diameter (mm)
Approx. 11.6
Specifi
cation
Standard outer
diameter (mm)
Approx. 7.0
Table 3.3 Restriction values by the baud rates
Maximum network length
Baud Rates
Thick cable
Thin cable
Drop line length
Total drop line
length
125 kbps
500 m max.
100 m max.
6 m max.
156 m max.
250 kbps
250 m max.
100 m max.
6 m max.
78 m max.
500 kbps
125 m max.
100 m max.
6 m max.
39 m max.
2] Restrictions when the trunk line is composed of both thick and thin cable
It is possible to combine both thick and thin cables to construct the trunk line.
However, the length of each cable type must satisfy the following relations.
In addition, if both types of cables are used, note that the value should not exceed the maximum current
capacity of each cable (Refer to the chapter 12).
Table 3.4 Maximum network length
Baud Rates Maximum network length
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 (thick): Length of thick cable
L (thin): Length of thin cable
Device Tap
Device
Device
Communication
power supply
Termination
resistor
Termination
resistor
The longer of the two becomes
the maximum network length.
Trunk line
Drop line