"LonWorks networks are intended for applications spanning home and building automation, plus factory automation and aircraft.

INTRODUCTION TO THE LONTALK® COMMUNICATIONS PROTOCOL

Kenneth P. Wacks

INTRODUCTION TO THE LONTALK® COMMUNICATIONS PROTOCOL

Kenneth P. Wacks, Ph.D.
Home Automation Consultant

"LonWorks networks are intended for applications spanning home and building automation, plus factory automation and aircraft."


Dr. Kenneth Wacks provides management and engineering consulting in home and building automation. He offers impartial and practical advice on business opportunities, network alternatives, and resources for product development. His clients have included SMART HOUSE, the Electronic Industries Association, the Intelligent Buildings Institute, electric and gas utilities, and manufacturers in the U.S., Canada, and Europe. For further information, please contact Ken at:
9 Pinewood Road,
Stoneham, Massachusetts
02180, USA
Tel: (617) 662-6211, Fax: (617) 665-4311, E-mail: kenn@alum.mit.edu


Introduction

This article is an excerpt from a report entitled, Home Automation and Utility Customer Services, written by Dr. Wacks and published by Cutter Information Corporation. Please see the Cutter web site ( www.cutter.com/energy/reports/homeauto.htm ) for an outline of the report and ordering information.


Figure 1.
Home Automation Networks

The full report is intended to guide energy utility companies in developing new customer services that use home automation networks. This excerpt focuses on the creation and definition of the LonTalk protocol. An article in the August issue of HTINews summarized the CEBus® protocol. The full report covers additional protocols including BatiBUS, European Home Systems, European Installation Bus (EIB), the Home Bus System from Japan, Home Electronic System (HES, an international standard), SMART HOUSE®, and X-10®, as shown in Figure 1.

The Formation and Marketing of Echelon

The Echelon Corporation of Palo Alto, California was formed in 1988 and funded by venture capitalists to develop communications technology and a protocol for interconnecting sensors, actuators, and controllers. Echelon has raised more than $80 million in capital and mounted a world-wide marketing effort resulting in extensive product exposure. Many manufacturers are adopting Echelon communications for building and factory automation products. The company is marketing heavily to the utility industry since they believe that utilities may help propel home automation into a major business.

Echelon offers hardware, firmware, and software components, plus tools for constructing networks. Such a network is called a LON®, for Local Operating Network. Echelon chose this term to distinguish the network from a LAN, or Local Area Network, developed for computer networks and office automation. A protocol called LonTalk® has been specified for operating a LON. The Echelon network with supporting hardware and software is collectively called LonWorks®.

Central to LON is a common interface for all devices attached to the network. This interface is called the Neuron® Chip, an integrated circuit manufactured to Echelon specifications and sold by Motorola and Toshiba. In 1996 Echelon introduced licensing arrangements for companies to design and manufacturer interface devices that substitute for the Neuron Chip.

LonWorks networks are intended for applications spanning home and building automation, plus factory automation and aircraft.

Relationship of Echelon to Standards Bodies

In May 1996, Echelon requested that the EIA (Electronic Industries Association) create a new committee to consider home automation standards in addition to CEBus. The EIA established the Home Control Systems (HCS) Committee and solicited proposals for work. Echelon proposed that a protocol based on the LonTalk protocol be accepted as a standard. HCS authorized technical committee HCS-1 to evaluate LonTalk. The HCS-1 Committee is writing a three-part standard based on LonTalk and designated EIA-709. Balloting of the proposed standard is expected this year.

In the field of building automation, the BACnet standard has been developed by a committee of ASHRAE, the American Society of Heating, Refrigerating, and Air-Conditioning Engineers. BACnet is intended to interconnect sensors, actuators, and controllers for HVAC (Heating, Ventilating, and Air-Conditioning) equipment in buildings. BACnet includes a common message set and provisions to accommodate various local area network standards for transporting messages from one device to another.

BACnet transmits these messages over a variety of specified networks. Some are commonly used in office automation, such as Ethernet. The lower two OSI (Open Systems Interconnect) layers of the seven-layer LonTalk protocol are referenced as one of five options for transporting BACnet commands.

Overview of the LonTalk Protocol

Architecture and Topology

LonTalk networks accommodate a variety of media for transmission. Nodes, such as appliances, switches, and sensors, may be connected to any medium provided the node contains the appropriate hardware and firmware. Transceivers for power line carrier, radio frequency, and twisted-pair wires have been announced by Echelon. They operate at speeds that are optimized for each medium, ranging from about 4000 bits per second (bps) for power line carrier to 1.25 million bps (the latter is for twisted-pair wires of limited length). Other manufacturers offer LonTalk transducers for coaxial cable and fiber optics. A LON network is intended for device control and does not support the distribution of audio or video analog or digital data.

LonTalk supports logically separate networks that may share a medium, such as the power lines or radio. In LonTalk each logical network is called a domain. LonTalk accommodates broadcast addressing to reach all nodes in a domain or in a subnet. Group addressing is also supported. A node may be a member of multiple groups.

Event Notification

The nodes on a LON network are each programmed to report specific internal data to one or more designated nodes. These reports are issued as a result of state changes or scheduled events. The addresses of recipients of a state change notice in Echelon are coded in an internal table of the Neuron Chip by a configuration tool. Reporting based on state changes is commonly done in building control systems. A typical example is a thermostat that alerts a furnace controller when the temperature decreases more than a threshold amount. The data reported are formatted into Echelon-defined network variables, called Standard Network Variable Types (SNVTs).

Thus, Echelon has chosen a data-oriented application protocol. This contrasts with the approach in other protocols, such as CEBus, of sending messages containing commands from appliance to appliance. The differences are highlighted in Figure 2. For example, a CEBus thermostat might command a furnace to turn on by sending a message to an address that could be determined dynamically. In contrast, a LonTalk thermostat would send a temperature change notice to a pre-specified device, such as a furnace, where an internal program determines whether to turn on the furnace.

LonWorks Development Tools

Echelon has developed a variety of components for creating a LonWorks network. Among these components is a collection of tools, called LonBuilder®. No other home automation developer offers such an extensive array of support tools yet.

A LonBuilder Development Station is intended for creating custom interfaces for devices that will communicate using the LonTalk protocol via a LON network. This allows a developer to select a communications medium and to program Neurons for specific applications, to test and debug the devices, to configure a network, and to analyze the network operation. The Development Station accommodates plug-in modules sold by Echelon for emulating a LON network. Personal Computer (PC) software is provided for programming these modules.

After a network application has been designed on a LonBuilder Development Station, the actual device nodes can be programmed using a LonBuilder Programmer connected to a PC. Application Layer objects may be programmed in a Neuron Chip using Neuron C, a custom version of the C programming language. Neuron C is a cross-compiler and debugger for Neuron Chips and facilitates programming the I/O ports on the chip.

A device application plus the LonTalk protocol may be contained entirely within a Neuron Chip. Applications too large for a Neuron Chip may be programmed in an external processor provided the Neuron firmware is altered with the LonBuilder Microprocessor Interface Program. These options are illustrated in Figure 3.

Once the Neurons and any associated microprocessors or PCs have been programmed, the network is configured with one of the LonManager® tools. A variety of LonManager Application Programming Interface libraries is offered for PCs running DOS and Windows. Software modules can download addresses, manage and analyze the network topology, load application programs into Neuron Chips, simulate data and messages, and retain information about network operations. Additional software functions include bringing nodes on and off line, configuring routers, and establishing keys for message authentication.

The LonManager Application Programming Interface provides these functions during application development in a laboratory or during manufacturing. Separate PC software modules called NetProfiler and NetMaker support field network management. They allow installation of nodes and connection to the network, verification of network operation with the nodes currently installed, and maintenance of the network. A network management tool is required if nodes are to be added or moved in the field. This tool may be embedded in the initial installation, for example in a monitoring station, or brought to the site when needed. Neuron Chips respond to configuration messages. A new tool, the NSS-10 module, periodically searches for added nodes and helps the user configure the network.

Institutional and Corporate Support for LonWorks

Echelon offers a suite of development tools for companies to explore networking with LonWorks. According to Echelon about 2500 companies have purchased development kits and hundreds of them are planning products using LonWorks or are providing development services.

About 150 companies have joined a users group called the LonMark Interoperability Association. This organization was established by Echelon to:

  • Promote LON product interoperability.
  • Offer product conformance testing.
  • Allow members to influence LonWorks products.
  • Promote LonWorks-based products.

The LonMark Interoperability Guidelines must be followed for products to be certified and carry the LonMark logo. These guidelines cover programming the Echelon components and attached protocol microprocessors. Echelon offers product conformance testing services plus a self-certification kit. In order to use the LonMark logo, the developer pays a fee based on company size, plus a fee per product tested for conformance.

© Copyright 1997, Kenneth P. Wacks


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