14
IM702-3
Doubly Terminated Topology Restrictions
The restrictions on doubly-terminated bus topology are as follows:
1.
The maximum number of nodes per segment is 64.
2.
The maximum total bus length depends on the wire size (see Qualified Cables for details)
Wire Size
Maximum Cable Length
24 AWG
2952 ft (900 m)
22 AWG
4590 ft (1400 m)
16 AWG
8855 ft (2700 m)
3. The maximum stub length is 9.8 ft (3 m). The length of the cable harness stub is 7.2 ft (2.19 m).
Note:
A stub is a piece of cable that is wired between the node and the bus. See Figure 9. Note that if the bus is wired
directly to the node, there is no stub, and thus the stub length is zero. If you are wiring to a field terminal strip on a
unit, be sure to account for any factory wiring between the terminal strip and the controller. This wiring is
considered part of the stub.
4. Two terminations are required in each segment. One must be located at each end of the bus.
Physical Network
Qualified Cables
Echelon has qualified three twisted-pair network communications cables that are available from a large number of different
sources. Refer to Echelon LonWorks FTT-10A Free Topology Transceiver Users Guide. See Reference Documents for part
number. Some local codes or applications may require the use of plenum rated cable. The following cables meet this
specification.
1.
TIA568A Category 5 cable (24AWG/0.51mm)
2.
NEMA Level IV cable (22AWG/0.65mm)
3.
Generic 16AWG (1.3mm) (similar to Belden 85102)
Do not install the cable in the same conduit with power wiring. The temperature of the cable must not exceed 131
°
F (55
°
C).
Note:
Ideally, you should connect two controllers with one continuous piece of cable in order to reduce the risk of com-
munications errors. If you must splice the cable, use crimp-type butt connectors (good) or solder (best). Do not
use wire nuts.
Network Cable Termination
LonWorks network segments require termination for proper data transmission performance. The type and number of
terminations depend on network topology. Refer to Echelon LonWorks FTT-10A Transceiver User’s Guide. See Echelon’s
Reference Documents for part number.
Addressing and Establishing Communications
LonWorks Network Addressing
Every Neuron Chip has a unique 48-bit Neuron ID or physical address. This address is generally used only at initial
installation or for diagnostic purposes. For normal network operation, a device address is used.
Device addresses are defined at the time of network configuration. All device addresses have three parts. The first part is the
Domain ID, designating the domain. Devices must be in the same domain in order to communicate with each other. The
second part is the Subnet ID that specifies a collection of up to 127 devices that are on a single channel or a set of channels
connected by repeaters. There may be up to 255 subnets in a domain. The third part is the Node ID that identifies an
individual device within the subnet.
A group is a logical collection of devices within a domain. Groups are assembled with regard for their physical location in
the domain. There may be up to 256 groups in a domain. A group address is the address that identifies all devices of the
group. There may be any number of devices in a group when unacknowledged messaging is used. Groups are limited to 64
devices if acknowledged messaging is used.
A broadcast address identifies all devices within a subnet or domain.
