Modbus is a serial communications protocol published by Modicon in 1979 for use with its Programmable Logic Controllers (PLCs). Simple yet robust, it has since become one of the de-facto standard communications protocols in the industry, and it is the most commonly available means of connecting industrial electronic devices. The main reasons for its extensive use in the industrial environment are:
Modbus allows for communication between many devices to be connected to the same network. For instance, a system that measures temperature and humidity communicates the results to a computer. Modbus is often used to connect a supervisory computer with a Remote Terminal Unit (RTU) in Supervisory Control And Data Acquisition (SCADA) systems. Many of the data types are named from their use in driving relays, as a single-bit physical output is called a coil, and a single-bit physical input is called a discrete input or a contact.
BACnet was designed to allow communication between building automation and control systems, it is widely used in applications such as heating, ventilating, and air-conditioning control, lighting control, access control, fire detection systems as well as their associated equipment. The BACnet protocol provides mechanisms for computerized building automation devices to exchange information, regardless of the particular building service they perform.
The BACnet protocol defines a number of services that are used to communicate between building devices. The protocol services include “Who-Is”, “I-Am”, “Who-Has”, “I-Have”, which are used for Device and Object discovery. Services such as Read-Property and Write-Property are used for data sharing. The BACnet protocol defines a number of Objects that are acted upon by the services. The objects include Analog Input, Analog Output, Analog Value, Binary Input, Binary Output, Binary Value, Multi-State Input, Multi-State Output, Calendar, Event-Enrollment, File, Notification-Class, Group, Loop, Program, Schedule, Command, and Device.
OPC is the Open Productivity & Connectivity in industrial automation and the enterprise systems that support the industry. Interoperability is assured through the creation and maintenance of open standards specifications.
There are currently seven standards specifications completed or in development. Data Access Specification was designed based on Microsoft’s OLE COM (Component Object Model) and DCom (Distributed Component Object Model) technologies. This specification defined a standard set of objects, interfaces and technologies, which then form the framework for software products to be developed, such as the Data Access, Alarm Events, Batch, Data eXchange, Historical Data Access, Security, XML-DA, Complex Data & Commands etc.
Simple Network Management Protocol (SNMP) is an Internet-standard protocol for managing devices on IP networks. Devices that typically support the SNMP are routers, switches, servers, workstations, printers, modem racks, and so much more. It is used mostly in network management systems to monitor network-attached devices for conditions that warrant administrative attention.
SNMP is a component of the Internet Protocol Suite as defined by the Internet Engineering Task Force (IETF). It consists of a set of standards for network management, including an application layer protocol, a database schema, and a set of data objects. In addition, SNMP exposes management data in the form of variables on the managed systems, which describe the system configuration. These variables can then be queried (and sometimes set) by managing applications.
Extensible Markup Language (XML) is a set of rules for encoding documents in machine-readable form. It is defined in the XML 1.0 Specification produced by the W3C, and several other related specifications, all gratis open standards.
The design of XML is built ground simplicity, generality, and usability over the Internet. It is in a textual data format with strong support via Unicode for the languages of the world. Although the design of XML focuses on documents, it is widely used in web services and other platforms for the representation of arbitrary data structures.
Many application programming interfaces (APIs) have been developed and are now used by software developers to process XML data and several schema systems, which exist to aid in the definition of XML-based languages.