Modbus protocol


Modbus is a communication protocol which is used with programmable logic controllers. This communication protocol was published by a firm named Modicon in 1979. It has now become the most de facto standard protocol in the industry. Modbus is now very commonly used as a means to connect the industrial electronic devices. This protocol is very easily available as it is very extensively used. There are certain important reasons for the use of Modbus rather than use of other communication protocol. These are as follows:

1.This protocol is published openly and is royalty free.
2.It is an easiest way to setup an industrial network.
3.This protocol moves raw bits without any restrictions.

modbus protocol

modbus webserver

Modbus can be used for various communications. It can be used for communication between devices which are connected to a particular network. For example, a system measuring the speed of the wind will transmits the data collected to a computer for records. Modbus as a communication protocol is used as a connection between the main computers and it is done with the help of Remote terminal unit (RTU) and data acquisitions (SCADA) systems.

There exist many editions of the Modbus. Various Modbus versions are used for Ethernet and also for the serial port. It is also used for the networks which support the IP, i.e. the internet protocol. Many of the Modbus devices commune with the help of a serial EIA-485 physical layer. Various versions of Modbus are as follows:

1. Modbus RTU – it is used for serial communications. This version of Modbus is normally implemented for use in communication.
2. Modbus ASCII – It is as a serial communication and the message transmitted are framed by a colon and a trailing new line.
3. Modbus TCP – this version is used for the communication between TCP networks.

The function calls and data model are same for these versions. The only difference between them is that the encapsulation varies for all. And also the frame formats varies for each of them.

Every device which communicates uses Modbus with a particular address. A Modbus command is used in various networks. This command has the particular device address and that device will only act on this command. All these command have the checking information and it make sure that the message comes undamaged. There is also a Modbus member organisation which can be joined by the large and small suppliers, system developers etc.

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