LonWorks to Modbus RTU QuickServer Gateway

• Modbus Application Protocol Specification V1.1a
• Modbus Messaging Implementation Guide V1.0a
• Modbus Messaging Implementation Guide V1.0b
• Modbus Serial Line Implementation Guide V1.0
• Modicon Modbus Protocol Reference Guide PI–MBUS–300 Rev. J (Modbus 300)

Reading Vendor Modbus Maps

If you are reading the documentation for sensor blocks, valves, and other devices, you must keep in mind that some vendors may document their hardware in different ways.

According to the Modbus standard, addresses are simply integers from 0 to 65,535 with the different address ranges being referred to as coils, holding registers, etc. However, some vendors will document their hardware using numerical prefixes which are not actually part of the Modbus address. This originated from some models of PLCs which used the Modbus communications protocol, and which also used numerical prefixes in their internal data table. This is similar to using “I”, “Q”, “V”, etc. as address prefixes in IEC type PLCs.

However, it is important to remember that these numerical prefixes are documentation methods and are not part of what the Modbus protocol itself sends as part of the messages. A difference in documentation methods does not affect the compatibility of the protocol itself.

These prefixes are they mentioned anywhere in the Modbus standard, but the following shows how they are typically used in documentation based on this older convention:

• 0xxxx – Coils.
• 1xxxx – Discrete inputs.
• 3xxxx – Input registers.
• 4xxxx – Holding registers.

Note that there is no 2xxxx address prefix.

In addition to numerical prefixes, some documentation will refer to protocol addresses (addresses start at 0), while other documentation will refer to data model addresses (addresses start at 1). That is, the first holding register may be 0 or 1 (or 40000 versus 40001 using prefixes). However, this has no bearing on what gets sent over the wire as a Modbus message. For a Modbus protocol message, the lowest address is always “0”, not “1”.

Scaling in Modbus

Modbus does not provide a method for transporting large or Floating Point numbers or a mechanism for scaling analog values. A 16 bit word can only contain values in the range 0-65535. Only whole numbers are permitted. To work around this many server device manufacturers use multipliers and document them in their manuals. For example, to report a temperature of 58.5 the device reports a value of 585, and makes a note in the manual that the master should scale by 10. This scaling is achieved by adopting a convention between the client and the server.
What about large numbers > 65535
Modbus does not provide a mechanism but 3 important schemes are widely used.

Long Integers – Two consecutive 16 bit words are interpreted as a 32 bit long integer.

MK10 values – Two consecutive words are used. The 1st reports the number of units and the 2nd reports the number of 10,000’s.

Floating Point Numbers – Two consecutive words are used and a scheme. These schemes are conventions and not all servers or clients support them.

The protocol does not identify these big numbers. Only the vendor docs do.
What we mean by this is – if you look at the byte stream in a Modbus message there is no way of telling whether you are looking at two consecutive 16 bit words, or two consecutive words that should be interpreted as floating point, long or MK10 formats. Because of this you always have to look to the vendor docs.

Port Expansion

FieldServer can easily be configured to allows a Modbus RTU client to talk to a ModbusTCP server and vice versa. You do not need to tell the FIeldServer which registers to map from one to the other. You simply configure the FieldServer telling it which port and protocol to use for each node.

In port expansion mode configuration can be moinimal. Tell the gateway which nodes are on which port and set the port settings.

Scaling / Bit Packing

FieldServers can scale data and manipulate values using some binary logic and arithmetic functions. Scaling can be applied to each block of Modbus Data read / served.

• Move to change type : Convert from any FIeldServer Data Type to any other.
• Move to pack/unpack bits and bytes: It’s possible to address each bit in a 8,16 or 32 bit data element by using the packed data types.
• Move to change byte/word order: Handle the endianess of the remote system easily.
• Convert to/from Float, MK10, IEE754, 32 bit, 16 bit, 8 bit numbers
• Move conditionally:
• Perform Arithmetic Operation: + – * div sqrt, sqr ,
• Perform Binary Logic Operation: And, Or, Not, >, >= , <, <=

Most functions can be configured to occur on a configurable period or on update of the data source.

Supported Data Types

Bit

Byte

16 Bit Integer Signed

16 Bit Integer Unsigned

32 Bit Integer Signed

32 Bit Integer Unsugned

32 Bit Packed Bit

8 Bit Packed Bit

4 byte FLoating Point Numbers

Supported Modbus Functions

01 Read Discrete Output Status (0xxxx)
02 Read Discrete Input Status (1xxxx)
03 Read Output Registers (4xxxx)
04 Read Input Registers (3xxxx)
05 Force Single Coil (0xxxx)
06 Preset Single Register (4xxxx)
15 Force Multiple Coils (0xxxx)
16 Preset Multiple Registers (4xxxx)

Flavors of Modbus

RTU:

Common
Binary Protocol.
Active Master-passive Slave
Serial
Supported by FieldServers, QuickServers, CAS gateways

ASCII:

Similar to ModbusRTU but for each byte in an RTU message, there are 2 bytes in an ASCII message. The 2 bytes are the humand readable form of the single hex byte.
Eg RTU byte = 0x03 (Hex). ASCII bytes = ‘0’ and ‘3’ ie 0x30 and 0x33
Active Master-passive Slave
Serial
Supported by FieldServers, QuickServers

Jbus:

Modbus had the limitation of a max of 9999 items of each type. Ie only 9999 holding registers. However the protocol message allows 65k items to be addressed. JBUS allows all 65k items to be read/written. Other than that it is identical to RTU
Active Master-passive Slave
Serial
Supported by FieldServers, QuickServers, CAS gateways

TCP/IP:

Uses TCP/IP connection based Ethernet communications
Encapsulates RTU messages and adds a header.
A single slave can respond to multiple masters
Many slaves ignore the NodeID field in the message.
Supported by FieldServers, QuickServers, CAS gateways

MB Plus:

Proprietary coax networking layer
2 Mbits/sec
Supported by FieldServers, CAS gateways

A set of services is offered by the LonWorks Protocol that enables all devices in the network to transmit and receive messages to and from other devices via their application program— requiring no acquaintances with network topology or the other devices’ names, addresses, or functions. Besides, LonWorks Protocol can be made to deliver authentic, high priority messages within delimited transaction times. Moreover Network management services allow remote network management tool’s interaction with devices over the network; making them capable to reconfigure network addresses and parameters, download application programs, report network problems and Start/stop/reset device application programs. Consequently it’s relatively easy to employ LonWorks network over any medium, including power line, twisted pair, radio frequency (RF), infrared (IR), coaxial cable, and fiber optics.

Lonworks is another communications protocol useful in building automation applications. The protocol was developed by the Echelon Corporationin the late 1990s. Lonworks originally transformed from Echelon’s earlier “Lontalk”, and was submitted to the American National Standards Institute (ANSI) for acceptance. Lonworks was designed on a low bandwidth platform for networking devices through powerlines, fiber optics, and other media.

The entire Lonworks package consists of the following components by the Echelon Corporation:

• Lonworks – communications protocol (ANSI/EIA 709.1, and others).
• Echelon’s “Neuron” chip (Three 8-bit inline processor). Two are used by Lonworks, and one as a general application processor.
• Twisted-pair and/or powerline transceivers to transmit Lonworks protocol.
• LNS Network Operating System is the required software.
• Internet connectivity through Standard Network Variable Types (SNVTs) or with LonMark profiles.
• LonMaker allows interoperability among devices.

Lonworks has various advantages and disadvantages. The advantages include:

• Less architecture at the device level.
• Numerous developers of Lonworks products in the market.
• Lonworks devices are close to “plug & play” ability, but still far from achieving interconnectivity in today’s computers using Microsoft Windows.

The disadvantages of Lonworks are presented in the following list:

• Less architecture causes controlled devices and variables to be connected to a separate control device. Most designers do not recommend this type of architecture because network interruptions could eventually produce system failures.
• The protocol is proprietary, and not truly open to the public. Only actual members, mostly manufacturers are included in standard development(s).
• Extensions within Lonworks are allowable only through the LonMark Consortium.
• Hardware specific, and requires the Neuron chip for network movement of the protocol.

Amongst the extensive range of LonWorks technology applications the vital nine are listed below:

• Semiconductor manufacturing
• Lighting control systems
• Energy management systems
• Heating/ventilation/air-conditioning systems
• Security systems
• Home automation
• Consumer appliance controls
• Public street lighting, monitoring, and control
• Gas station control

A P2P (peer to peer) architecture is undoubtedly the preeminent way to build control networks. Being exclusive of a single master control, P2P-based control network confers high reliability and high performance to its users. Unlike other control networks, in P2P architectures, there is absolutely free and open communication between network devices which automatically puts a stop to the system collapses that could occur whenever the master stops working.

A processor identified as Neuron chip embracing three 8- bit inline processors designed by Echelon is well optimized for control network devices. Out of three processors: two are committed for the communications protocol and one is a general-purpose applications processor. Standardization of the variables used to illustrate physical things to LonWorks is maintained by LonMark International and each standard is known as Standard Network Variable Types (SNVTs). LNS Network Operating System is a mandatory software component of open control systems which ensures an open environment for extending, maintaining, and managing LonWorks based system

LonWorks is not just a protocol or physical layer for communication but an exclusively designed networking technology platform to install, maintain, monitor and sense various automation and control applications. Essentially LonWorks was established for a range of automation functions within buildings such as lighting and HVAC. Invented by Echelon Corporation, the fundamental communications platform, twisted pair signaling technology, power line signaling technology, and IP tunneling method constitutes a global standard documented ISO/IEC 14908.

LonMaker is a Windows GUI based network/device management tool for Echelon LonWorks. It can be used for initial network setup and functioning as a management console on a completed network.

Purchase from Echelon.

The communications between all Lonworks devices is done by means of a proprietry chip (The Neuron chip) made according to one design by one company according to one standard which it wrote on its own. It’s obvious that there are so many less aspects of the data communications process that can go wrong when there is a single entity involved. When a device vendor implements a Lonworks System Interface he simply has to implement the application layer of the data communication process. For almost all other protocols the device vendor must implement the physical layer, data link layer, the Network Layer, The transport Layer, The Session Layer, the Presentation Layer and the Application Layer. You can see how many more areas of risk there are.

When Echelon released the standard, their license terms required anyone who implements it to implement the full standard. The fact that other vendors can’t cherry pick features and services means that even when implemented by other vendors you still have the same strong chance of success.

Lonworks – a wide ranging term generally applied to describe the whole technology developed by Echelon. It is used frequently and ambiguously.
LonTalk – A registred trademark belonging to Echelon. They use it as the name of the protocol used for data communications in a Lonworks system. Ie. It is the brandname protocol. Echelon released this protocol so it could be adopted as a standard – ANSI-approved standard EIA/CEA-709.1-A-1999 – SO/IEC Standard 14908 or European standard EN14908.

How to Commission and Bind using Lonmaker. CAS can configure Lonworks gateways so Commissioning and Binding can be avoided. Call our Tech Sipport for more info.

https://www.youtube.com/watch?v=u_mzAdszviI

https://www.youtube.com/watch?v=w3QeimYx94I

https://www.youtube.com/watch?v=H76n1-lcrhI

https://www.youtube.com/watch?v=SEcAx6xy3is

https://www.youtube.com/watch?v=dFyyKNmGVB4

https://www.youtube.com/watch?v=B_Cs1clgNzM

https://www.youtube.com/watch?v=29cuWwVKNdA

https://www.youtube.com/watch?v=vm2Ss72C5bg

Another useful utility is XIFDUMP. It is a report generator (DOS), and it allows you to generate reports (text file) from a XIF files.

Download XIFDUMP:

XIFDUMP