What is Modbus and how is it used in IoT?

What is Modbus?

Modbus is a serial communication protocol for use with programmable logic controllers. It is typically used to transmit signals from instrumentation and control devices back to a main controller; or data gathering system, for example a system that measures temperature and humidity and communicates the results to a computer, according to Simply Modbus.

How does it work, and why use it for IoT?

The method is used for transmitting information over serial lines between electronic devices. The device requesting information is called “master” and “slaves” are the devices supplying information. In a standard Modbus network, there is one master and up to 247 slaves, each with a unique slave address from 1 to 247.

According to Intel, communication between a master and a slave occurs in a frame that indicates a function code. The function code identifies the action to perform, such as read a discrete input; read a first-in, first-out queue; or perform a diagnostic function. The slave then responds, based on the function code received, with a response indicated by a set of bytes. Slaves can therefore be intelligent devices or simple devices that represent a single sensor.

Because of this operation, systems based on the protocol are critical parts of the industrial “internet of things” for automation and control, housing valuable information that can be unlocked and used by analytics and enterprise systems.

The protocol is commonly used in IoT as a local interface to manage devices. It is an open protocol that is free for manufacturers to build their equipment into, and is now the most commonly available means of connecting industrial electronic devices, according to Simply Modbus.

Benefits of using Modbus

These are some advantages of using Modbus, as outlined by the Modbus Organization:

• If a Modbus driver is already installed and the user is familiar with Ethernet and TCP/IP sockets, a driver can be up and running and talking to a PC in a few hours. Development costs are said to be low; minimum hardware is required; and development is said to be easy under any operating system.
• There are no “exotic” chipsets required and the system can use standard PC Ethernet cards to talk to newly implemented device; as the cost of Ethernet falls, there should be a cost reduction in hardware; and users are not tied to one vendor for support, but can benefit from current developers.
• The specification is available free of charge for download, and there are no subsequent licensing fees required for using Modbus protocols.
• Interoperability among different vendors’ devices and compatibility with an installed base of compatible devices.