Modbus is an open source protocol, which led to the widespread deployment of Modbus systems which are most frequently used for industrial applications. Multiple Remote Telemetry Units (RTUs) and/or Intelligent Electronic Devices (IEDs) that supports the Modbus protocol can be connected to the same physical network to create a Modbus network. A Modbus network, at its most basic, is a network of master and slave devices that communicate using the Modbus protocol. These Modbus networks typically utilize a serial connection while Modbus TCP/IP networks, which is made up of devices that supports the Modbus TCP/IP protocol, will usually use 10BaseT or faster for their connection.
A common Modbus network consists of having a single master and multiple slave RTUs and/or IEDs.
The master/slave address design of a Modbus network enables a Modbus master to communicate with a specific device by using its unique Modbus address. This unique identifier, the address, has a range of 1 to 247 and can be located at the beginning of the message that will be sent to the Modbus master.
A simple Modbus network can have up to 247 connected at one time the same network. Each of the 247 connected Modbus devices are assigned their own unique identifier which they will use to communicate with other Modbus devices.
Note: Modbus TCP/IP networks can generally support more devices than a traditional Modbus serial network.
In a master and slave configuration, the communication stream is controlled by the Modbus master. The Modbus master can request data from or write data to Modbus slave devices across the network using specific register and/or coil addresses. The Modbus slaves on the other-hand can only respond to the master's requests or commands as it is received.
The Modbus protocol has evolved into several different variations. These variations are designed to support Modbus network communications over a variety of physical network layers. These variations include Modbus RS-232 and Modbus RS-485, which will support different types of serial connections.
There is another variation of the Modbus protocol called Modbus TCP/IP.
The Modbus TCP/IP specification was created in response to the expanding usage of Ethernet. Since TCP/IP is the transport protocol of the Internet, Modbus TCP/IP, which is simply the Modbus wrapped with TCP/IP, can be used to communicate over a Modbus network structured with an IP connection.
Modbus TCP/IP provides a huge set of capabillties because of its compatibility with other TCP/IP support devices and software.
For example, a Modbus TCP/IP device that is located halfway across the world in a remote location can be still accessed through the Internet because of TCP/IP.
Two additional variants of the Modbus protocol are Modbus ASCII and Modbus RTU. These variations are optimized for use with ASCII equipment and with Modbus capable RTUs. Each of the aforementioned Modbus variants uses a slightly different communication format, allowing users to deploy a Modbus network in the variant that is the most compatible with their other equipment.
A Modbus network should be developed using the most advanced Modbus monitoring technology. With advanced Modbus monitoring systems, you can provide automatic page and email notifications of all your alarms. With location and repair information sent directly to your technicians, you can handle network problems more quickly and efficiently. The most advanced systems will also allow you to bring in alarms from other protocols and can display all of your important notifications in a single window that can be monitored by a single network operator.
A master system such as the T/Mon NOC can be what you need for your Modbus network. It is a multifunction and multiprotocol system that provides a multitude of features all in a single-platform.
Modbus, SNMP, and ASCII are just a few of the many protocols supported by the T/Mon NOC. The T/Mon NOC comes with T/Mon GFX which is a graphically user interface for displaying alarms visually on a layered geographical map. Built to be the solution for a wide range of problems, it could be exaclt what you need.
Modbus is a protocol developed in 1979 by Modicon for use with their Programmable Logic Controller (PLC). It is a free and open protocol which helped get the protocol adopted by many users and devices.
A serial connection, or a serial communication, is the process of sending data one bit at a time over a connection or communication channel in a sequence.
10BaseT is a twisted-pair cable that is used for LAN and can achieve speeds of up 10Mbps.
A Remote Telemetry Unit (RTU) is a device created for monitoring and reporting events that occurs at a remote site. The typical events that will be monitored are temperature, humidity, and voltage levels. Almost anything can be monitored with an RTU. Information regarding these events are collected by the RTU and then sent out to a master station like the T/Mon.
An Intelligent Electronic Device (IED) is a microprocessor-based controller that has advanced local control intelligence.
TCP/IP is used as the transport protocol of the Internet and is made up of two different protocol layers. The first layer, the transport layer, called the Transmission Control Protocol (TCP) is used to break up a message or file into smaller pieces of data called packets that are then sent over the Internet. It is also responsible for rearranging the packets when it receives them. The second layer, the Internet layer, called the Internet Protocol (IP) is used for addressing the packets so that the packets will get to the correct destination.
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