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Origins of MODBUS?
Looking for basic information about MODBUS and its use
1 out of 1 members thought this post was helpful...

Hi

can any body explain why MODBUS communication came into existence? Is it used for 3rd party communication? how can v make 3rd party communication? & also in PLC some signals (analog or digital) are taken through modbus, why it is done so? why modbus is needed? v can take all signals through AI, AO, DI & DO modules.

please reply

By theengineer on 29 December, 2015 - 6:56 pm

Modbus is a serial based communication protocol that has been widely used in industrial automation industries. Modbus allows for communication between many devices connected to the same RS-485 network, for example, a system that measures temperature and humidity and 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.

In a sense, you can look at Modbus as a language. In order for one device to communicate to another or even to a PC, it needs to speak the same language.

I found this video that explains Modbus and it's applications:
http://www.icpdas-usa.com/modbuswebtraining.php?r=lucy

I hope this helps.

By Lenore Tracey on 30 December, 2015 - 2:49 pm
1 out of 1 members thought this post was helpful...

You can find information about the history of Modbus, and freely download the protocol specification as well as implementation guides on the website of the Modbus Organization: http://www.modbus.org.

The organization also maintains a directory of Modbus suppliers and Modbus devices, as well as links to many technical resources.

Best of luck!

The advantage of using Modbus communication over hardwired signals (AI, AO, DI, DO) between two systems is that you can transmit a large number of signals over Modbus link which can be as simple as a single pair cable. Two systems connected through Modbus can share hundreds of data points over a single physical connection. In case of hardwired signals, you need as many IOs as the data points you want to exchange on both systems. This will increase your hardware cost enormously and also lot of hardwiring between systems.

Another advantage of Modbus is that the communication is digital. So there is no loss of accuracy or fidelity. So, if a system is reading a pressure of, say 54.51 bars, it will be sent exactly like this on the other system. This accuracy is not possible with AO/AI signal combination because of accuracy lost in D-A and A-D conversion.

Moreover, the Modbus is not just used for point-to-point communication, but you can connect upto 32 devices on one Modbus network which will communicate with one Modbus master. This means that the master can exchange a large amount of data with every slave device on the network, individually.

Modbus protocol was originally developed for serial communication (RS232, RS422, RS485). But now it is also implemented over Ethernet as Modbus TCP and allows further flexibility and ease of installation.