234 • LON

Network architecture – Principles and Regulations

combination of these two are possible. A matching resistor is required to prevent signal reflections from interfering with the data traffic on the bus.

Warning!

To avoid damage to or destruction of the hardware and to the software, ensure that the following wiring instructions are adhered to:

–Select the wire routing such that capacitive, inductive and high frequency stray pick-up will not negatively affect signal transmission.

–Route signal and data cables separate from power cables.

–When routing cables outside of buildings, adhere to the lightning protection regulations! Here, amongst others, the protection of data lines against surge voltages by means of varistors or surge arrestors is concerned. If necessary, seek detailed consultation from your manufacturer of corresponding lightning and surge voltage protection systems regarding suitable components and their application. Remember that not only the network lines are endangered but also the supply voltage!

5.3.2Topology

By its various coupling possibilities, such as repeaters, routers, bridges or gateways, LON allows a versatile network topology and a quasi unlimited length with a maximum of 32,000 intelligent bus subscribers.

In addition, also the various transmission media, such as twisted pair, 230 V~ power cable, radio, infra-red and fibre optic cables, can be mixed.

With LON, the 230 volt supply voltage cables are routed separate from the bus cables (except the power line). In a special way of transmission ("Link Power") the data and the first supply voltage rate for the units are transmitted via a common cable pair. With the transmission form "free topology" the supply voltage and the data are transmitted via separate cable pairs.

To obtain the maximum freedom when designing the networks, transceivers for free topologies were developed. In addition to the bus structure, this allows the architecture of ringand star shaped networks and/or mixed topologies.

A total of 64 nodes can be connected to one bus segment.

For intended applications with a number of nodes exceeding the permissible maximum number of 64 per channel or for which the transmission distances are not sufficient, repeaters can be used.

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LON • 235

Network architecture – Principles and Regulations

Repeaters are used to refresh and amplify the bus signals. They can also be employed for branching and tree structures, however, we recommend to observe that the number of physical repeaters which are allowed to be installed between two communicating nodes is limited to one. As an alternative, a router can, of course, be integrated into the network, which is not subject to this limitation, not even when configured as a repeater. Please also remember that the transceivers of the routers/repeaters must also be counted as part of the 64 node limitation.

Fig. 5-2. Examples for network topology

5.3.3 Transceiver

The FTT-10 transceiver (Free-Topology Transceiver) used as standard in the LON coupler is compatible with the LPT-10 transceivers (Link-Power Transceiver). As such, there are further possibilities to be used for a network architecture.

With the FFT-10, a network with a data rate of 78 kbps, a number of nodes of 64, and a distance of 2700 m is possible with the bus topology and of 500 m with the Free Topology.

Tab. 5-1: Characteristic data for Transceiver FTT-10

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