Ba-modbus, Bacnet, OPC, ODBC, LonWorks conceptual analysis

1.Modbus

Modbus technology has become an industry standard. It was developed and developed by the Modicon company. Its communication mainly uses
rs232,rs485 and other communication media. It provides users with an open, flexible and standard communication technology that reduces
Development and maintenance costs.
Modbus communication protocol by the main device to establish a message format, the format includes the device address, function code, data address and out
Error checking. From the device must use the Modbus protocol to establish a reply message, its format contains the function code of confirmation, return data
and error checking. If the received data is faulted, or the requested command is not executed from the device, the slave will return the
Error message.
The Modbus communication protocol has its own message structure. Regardless of the network used to communicate, the message structure can be
System adoption and identification. With this communication protocol, you can ask other devices on the network, as well as reply to other devices
, you can also detect and report error messages.
During communication on the Modbus network, the communication protocol can identify the device address, messages, commands, and messages contained in the message.
Data and other information, if the agreement requires a reply from the device, a message is formed from the device and the
Modbus sent out.

2.BACnet

BACnet is a data communication protocol of Building automatic control system, which consists of a series of communication protocols related to software and hardware,
Specifies the mode of all conversations between computer controllers. The protocol includes: (1) The characteristics of the electronic signals used in the selected communication medium,
How to identify the computer URL, determine when the computer uses the network and how to use. (2) Error detection, data compression and coding to
and individual computer-specific information formats. Obviously, there are many ways to solve these problems, but two different modes of communication
The possibility of choosing the same protocol is minimal, so a standard is required. ISO (International Standardization Association) in 80
Open Systems Interconnection (osi〉 Basic Reference mode (open system
Interconnection/basic Reference Model abbreviation OSI/RM) is0‐7498 ".
OSI/RM is the most important of the ISO/OSI standards, which provides a common reference for the compatibility of other 0SI standards,
The design, realization and transformation of information processing systems provide a functional and conceptual framework. It is a total of
Guiding standards, but also the basis and premise of understanding other 0SI standards.
0SI/RM is divided into seven layers according to the stratification principle, namely physical layer, Data link layer, network layer, transport layer, conversation layer, presentation layer,
Application layer.
BACnet since it is an open computer network, it is necessary to refer to Osiam. But BACnet not from the lowest layer of the network
Redefine their own hierarchy, but choose the mature LAN technology, simplify the 0SI/RM, the formation of a wide range of LAN-tolerant simple
Single, practical, four-tier architecture.
Level four structure includes physical layer, data link layer, network layer and application layer.

The BACnet protocol consists of the following parts: The function of building automation equipment and the representation of information data, five kinds of standard LAN
Communication protocols and the protocols that they communicate with each other.

Introduction to the 3.OPC specification

The OPC (OLE for Process Control) specification, developed by OPC Task Force, was formally born in August 1996, with
February 1997 Microsoft launched the WINDOWS95 supported DCOM technology, September 1997, the newly established OPC
The OPC specification is modified by the Foundation, and some standards such as data access are added, and the OPC specification is further
Perfect.

"OPC based on Microsoft Company's Distributed interNet Application (DNA) architecture and Component Object
Model (COM) technology, designed for ease of extensibility. The OPC specification defines an industry-standard interface, which
Standards make COM technology suitable for application areas such as process control and manufacturing automation. "OPC Foundation Committee Chairman Dave
That's what Rehbein describes.
OPC is a communication standard using the ole/com mechanism as an application. Ole/com is a client/server model with
Language independence, code reuse, ease of integration and other advantages. OPC specification interface functions, regardless of the field equipment
form, and customers are accessing it in a unified manner, thus ensuring the transparency of the software to the customer and making the user completely
Out of the development of the low-level.
The software structure based on OPC
As the diagram shows, there must be an OPC interface between the application and the OPC server, and the OPC specification provides two sets of standard interfaces:
Custom standard interface, OLE Automation standard interface. OLE Automation standard interfaces are typically used in system design.
OLE Automation standard interface, and calls using OLE Automation technology, the technology for the OLE Automation technique described in the previous section
Postoperative The OLE Automation standard interface defines the following three-layer interface, which in turn contains the relationship.
OPC SERVER:OPC starts the server, obtains the starting class for other objects and services, and returns the OPC Group class to
Like
OPC Group: Stores group information consisting of several OPC item and is used to return the OPC item class object.
OPC Item: Stores information such as the definition of a specific Item, data values, status values, and so on.

Since the OPC specification is based on ole/com technology, the extended remote OLE Automation and DCOM technology support ole/com
TCP/IP and other network protocols, so that OPC customers, servers can be physically separated, distributed in different networks
node.

OPC specifications can be applied in many applications, as they can be applied to the physical setting of a SCADA or DCS system
The lowest layer of raw data, they can also be used to obtain data from SCADA or DCS systems to
In the program. In fact, the purpose of OPC design is to obtain data from a node on the network. Figure 4.2.2OPC Customer/Service
The application of OPC in SCADA system is also described in the service diagram.
Advantages of using OPC specification design system
In the development of a new type of microcomputer Telecontrol system, the data exchange of each computer and each module should be in accordance with the OPC Regulation
The "fan". Doing so has the following benefits:
The OPC specification is based on ole/dcom technology, while ole/dcom supports network protocols such as TCP/IP, so the
The sub-systems are physically separated and distributed across different nodes of the network.
OPC, in accordance with the object-oriented principle, encapsulates an application (OPC server) as an object and only
Port method exposed, customers in a unified way to call this method, so as to ensure that the software to customer transparency, so
The user is completely detached from the low-level development.
OPC realizes the remote call, makes the distribution of the application independent of the distribution of the system hardware, facilitates the system hardware configuration and
Make the system more extensive application.
Using OPC specification, it is easy to configure the system, simplify the system complexity greatly,

Improve the reliability and stability of software operation, easy to upgrade and maintain the system.
OPC specification of interface functions, regardless of the form of field equipment, customers are in a unified way to access, so that the real
The system is open and easy to interface with other systems.

4.LONWorks

U.S. echelon Company in December 1990 to the world launched the LONWorks Networks fully distributed Intelligent Control network
Technology. The network structure is customer/service type. LONWorks Technology is a general-purpose bus that can be used in industrial control systems simultaneously
Used in any layer of bus such as Sensor bus, Device bus, Field bus, and so on.
LONWorks Technology, in addition to the bus-type network structure, users can also choose any form of network topology. Network
Communication media can be twisted-pair, power line, fiber, wireless, infrared, etc. and can be in the same network
Mixed use.

5.LonTalk

The communication protocol used by LONWorks technology is called the LonTalk protocol. LonTalk agreement is followed by the International Organization for Standardization (ISO)
A defined Open Systems Interconnect (OSI) model. In the terms of ISO, the LonTalk protocol provides the OSI reference Model as defined
All seven levels of service. The LonTalk protocol supports networks that are segmented by different communication media. Media packages supported by the LonTalk protocol
Including twisted pair, power line, wireless, infrared, coaxial cable and optical fiber.

6.ODBC

Open database connection The acronym for Open Databases connectivity. A connection in the Microsoft wosa structure
Provides a common language for Windows-based applications to access network databases.

Ba-modbus, Bacnet, OPC, ODBC, LonWorks conceptual analysis