In this blog post, we will discuss what Modbus communication protocol is and the types of Modbus used in the industry.


What is a protocol?

First, let’s know what a protocol is. Protocol is the language used for communication technology, just like the language of our daily conversation. For example, we make an agreement called protocol, “1” is left, “2” is right, and I will give you a “1”. If you don’t learn this protocol, you only know that it is “1”, and if you have leant that, you will know that it means left.

What is Modbus protocol?

After comprehending the concept of “protocol”, let’s look at what Modbus protocol is. Modbus is a serial communication protocol, and it is a bus protocol published by Modicon Company (now owned by Schneider Electric) in 1979 for communication with its programmable logic controller (PLC).

Several versions of the Modbus protocol exist for the serial port and Ethernet and the most common are: ModBus TCP, ModBus RTU, ModBus ASCII and ModBus Plus.

ModBus ASCII protocol

ModBus ASCII protocol is based on ModBus RTU protocol, which converts instructions into ASCII characters for transmission. For example, ModBus RTU protocol needs to transmit “12”, which only needs one byte. ModBus ASCII protocol needs to convert “1” to “31” and “2” to “32”, and then it takes two bytes to transmit. Therefore, ModBus ASCII is inefficient and has a low utilization rate.

ModBus Plus protocol

ModBus Plus protocol, commonly known as MB+, is a high-speed fieldbus network, a typical token bus network and a local area network system especially for industrial control applications.

ModBus TCP protocol

ModBus TCP protocol is used to manage and control automation equipment. It covers the use of ModBus messages in “Intranet” and “Internet” environments using TCP/IP protocol. You can see it as ModBus RTU protocol running on Ethernet.

ModBus RTU protocol

ModBus protocol is a protocol running between devices, or we should say there must be ModBus RTU protocol between devices! This is stipulated in ModBus protocol, and the default mode must be RTU protocol. Frame structure generally consists of address, function code, data and check.

Why is Modbus protocol all the rage?

Up to this point, it doesn’t seem to see why the Modbus protocol can be so popular. Let’s find out together.

Modbus has become the industry standard of communication protocol in industrial field (De facto), and now it is a common connection mode (an industry standard) between industrial electronic devices. In addition, there are the three primary keys to its success:

  • Publicly published and without copyright requirements.
  • Easy to deploy and maintain
  • There are not many restrictions on changing local bits or bytes.

Modbus solution

Generally speaking, Modbus is a protocol for industrial control, which has three characteristics: free use, easy to use and easy to change, and has been widely used.

Because of the above characteristics, Modbus protocol has stood the test of time and is still being used in a wide range of fields, such as instruments and meters, intelligent high and low voltage electrical appliances, transmitters, programmable controllers, man-machine interfaces, frequency converters, field intelligent equipment and so on.

How is the Modbus used in the industry?

There comes the new-generation IoT edge gateway designed for industrial IoT. With pre-integrated industrial protocols such as Modbus TCP/RTU and IoT clouds like MS Azure and AWS, the IoT edge gateway makes it easy to collect data from different onsite devices, validate data and upload them to the cloud — and the configuration takes only a few minutes without any programming.

Modbus connection

The gateway can play the role of a Modbus Master and reads registers from a Modbus Slave device. The signals can be on both the RS485 link and also the Ethernet link.


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