What is MODBUS

The MODBUS protocol is an application layer protocol used primarily for communication between electronic devices in industrial environments. It defines a message structure that enables different devices to exchange data in a standardised way.The MODBUS protocol supports a wide range of transmission methods including, but not limited to, serial communication and Ethernet communication.The popularity of the MODBUS protocol is due to its openness and compatibility with devices from different manufacturers.

Data types supported by Modbus

The MODBUS protocol supports a variety of data types to meet the needs of different devices and applications. The following are some common MODBUS data types:

• Bit : Used to represent switching status or Boolean values.

• Integer : can be 8 or 16 bits, used to represent numeric values.

• Float : Used to represent decimal values.

• String : used to represent text information.

• Register : Used to store 16-bit data, either integer or float.

Each data type has a specific use and storage method. For example, bit data is often used to control the on/off state of a device, while registers are used to store more complex numerical information.

Scenarios of use are as follows

1. Bit

Usage Scenario

• Discrete Inputs (Discrete Inputs) : used to read the status information of the device, such as sensor on/off status, alarm signals, etc.

• Coil Status : Used to control the output devices, such as starting or stopping motors, opening or closing valves, etc.

2. Integer

Use scenarios

• Example : reading degrees from a temperature sensor (e.g. 25°C).

• 8-bit integer : not normally used directly in Modbus, but can be used as part of the internal processing of some devices.

• 16-bit integer (stored via registers) : used to represent various numerical information such as counter values, temperature values (integer part), pressure values, etc.

3. Float

Usage Scenario

• Example : reading degrees from a precision temperature sensor (e.g. 25.123°C).

• 32-bit floating point number (stored via two consecutive registers) : used to represent values that require higher precision, such as temperature, pressure, flow rate, and other measurements.

4. String

Usage Scenario

• Example : read the model or version information of the device.

• ASCII string (stored through multiple registers) : used to represent text information such as device ID, serial number, fault code description, etc.

5. Register

Use scenarios

Example

• Used alone : reads an integer value of the sensor (e.g. humidity percentage).

• Used in combination : reads a 32-bit floating point value of the sensor (e.g. humidity percentage with decimal point).

• 16-bit registers : can be used to store integer data or combined with other registers to store 32-bit data.

Summaries

In conclusion, MODBUS protocol makes data exchange between different devices simple and reliable by defining a unified data format and structure. It supports a variety of data types and can meet a variety of needs in industrial automation. With the development of Industry 4.0, the MODBUS protocol is constantly being updated and expanded to adapt to new technologies and application scenarios.

(Note: The above is reprinted from WeChat - Industrial Visualisation)