Figure 9. Combining Network Segments With A Repeater; Figure 10. Doubly Terminated Network Topology - McQuay MicroTech II Installation And Maintenance Manual

A network segment is any part of the free topology network in which each conductor is electrically
continuous. Each of the four diagrams is an illustration of a network segment. Some applications may
require two or more segments; see "Free Topology Restrictions.". If necessary, segments can be
joined with FTT-10A-to-FTT-10A physical layer repeaters. See Figure 9. Refer to Echelon
LonWorks FTT-10A Transceiver User's Guide for details. See Reference Documents for part
number.

Figure 9. Combining Network Segments With a Repeater

Free Topology Restrictions
Although free topology wiring is very flexible, there are restrictions. A summary follows, refer to the
Echelon FTT-10A User's Guide for details. See Reference Documents for part number.
1.
2.
Note:
3.
Doubly Terminated Networks
You can extend the maximum total cable length without using a repeater by using doubly-terminated
network topology. See Figure 10. The trade-offs are (1) this network topology must be rigorously
followed during the installation and subsequent retrofits and (2) two terminations must be installed at
the ends of the bus for proper transmission performance. Refer to Echelon LonWorks FTT-10A
Transceiver User's Guide for details. See Reference Documents for part number.
Note: Limitations to wire lengths apply and must be observed.

Figure 10. Doubly Terminated Network Topology

Doubly Terminated Topology Restrictions
The restrictions on doubly-terminated bus topology are as follows:
IM 735-0
Termination
The maximum number of nodes per segment is 64.
The maximum total bus length depends on the wire size (see "Qualified Cables" for details):
Wire Size Maximum Node-to-Node Length
24 AWG 820 ft (250 m)
22 AWG 1312 ft (400 m)
16 AWG 1640 ft (500 m)
The longest cable path between any possible pair of nodes on a segment must not exceed the
maximum node-to-node distance. If two or more paths exist between a pair of nodes (e.g., a loop
topology), the longest path should be considered. Note that in a bus topology, the longest node-
to-node distance is equal to the total cable length.
The total length of all cable in a segment must not exceed the maximum total cable length.
One termination is required in each segment. It may be located anywhere along the segment.
Termination
Termination
Maximum Cable Length
1476 ft (450 m)
1640 ft (500 m)
1640 ft (500 m)
Termination
13