Modbus is a crucial communication protocol in industrial automation, and its significance has extended to various applications, including electric vehicle charging. Imagine you have several devices in a factory, such as sensors, motors, and other equipment, and you need them to communicate with each other to coordinate their actions. To achieve this, you need a common language that all of them understand, and this is where Modbus comes into play.

Modbus: what it is and how it works

Modbus’s ability to facilitate communication between electronic devices in an efficient and reliable manner makes it an essential tool for optimising the functionality of our electric vehicle chargers. Its use ensures that devices can communicate and operate in harmony, improving both the efficiency and safety of charging systems.

Modbus is a communication protocol, which is essentially a set of rules that allows devices to exchange information. It is like a common language that enables different types of electronic equipment to understand each other.

The history of modbus

Modbus was created by Modicon (now part of Schneider Electric) in the late 1970s. It is an open communication protocol used for transmitting information over serial networks between electronic devices.

In a Modbus network, the device that requests information is called the master, while the devices that respond to these requests are known as slaves. This master-slave system allows for efficient and structured communication, where the master controls the network and the slaves respond to its commands.

Types of Modbus and how they work

Depending on the project’s requirements and the devices that need to be interconnected, different types of Modbus protocols are used. Below, we explain the most commonly used Modbus types.

Connection on the Trydan Board for Modbus

What Is Modbus RTU (Remote Terminal Unit) and How Does It Work?

Modbus RTU is a version of the Modbus protocol that uses binary encoding and robust error checking through CRC (Cyclic Redundancy Check). This protocol is widely used in industrial applications due to its simplicity and reliability. Data is transmitted in 8-bit bytes over serial connections, with speeds ranging from 1,200 to 115,200 bits per second, although most devices operate at speeds of up to 38,400 bits per second.

In a Modbus RTU network, a master controls communication with one or more slaves, each identified by a unique address. The master sends messages that include the address of the intended slave, and the slaves respond only if they recognise their address. This structure allows for organised and efficient communication, reducing errors and improving the reliability of automation systems. For instance, at V2C, we establish the Modbus RTU connection with Trydan.

Here are its features:

• Serial Transmission: It uses serial communication lines, such as RS-232, RS-485, etc.
• Compact Message Format: Messages are compact, allowing for faster and more efficient transmission.
• Binary Mode: Data is transmitted in binary format, meaning bits (0s and 1s) are used.

Advantages of Modbus RTU:

• Ideal for short to medium distances.
• Simple and cost-effective for small to medium-sized installations.

Limitations of Modbus RTU:

• Distance and speed limitations.
• A limited number of devices can be connected on the same communication line.

What is Modbus RS-485 (Recommended Standard 485) and how does it work?

Modbus RS-485 is an implementation of the Modbus protocol that uses the RS-485 communication standard for data transmission. RS-485 is a serial communication standard that stands out for its ability to allow long distances and multiple devices on a single communication line.

Compared to other standards, RS-485 offers significant advantages in terms of robustness and flexibility. It enables communication over distances of up to 1,200 metres and supports transmission speeds ranging from 300 to 10,000 bits per second, adapting to the various needs of industrial applications.

In a Modbus RS-485 network, the communication structure is usually master-slave, similar to that of Modbus RTU. The master device controls the network and sends messages to one or more slave devices, each with a unique address. The slave devices only respond to requests addressed to their specific address, enabling organised and efficient communication.

Here are its main features:

• Differential transmission: RS-485 uses differential transmission lines, which increase resistance to interference and improve signal quality over long distances.
• Multipoint: It supports the connection of multiple devices (up to 32 in most configurations) on a single communication line, facilitating network expansion.
• Adjustable speeds: Transmission speeds can be adjusted according to system needs, providing flexibility in network configuration.

Example of how Trydan communicates with this type of Modbus

Advantages of Modbus RS-485:

• Long-distance communication: Ideal for applications requiring long-distance data transmission without significant quality loss.
• Ability to connect multiple devices: It allows the connection of numerous devices on a single communication line, simplifying network infrastructure.
• Interference resistance: Differential transmission reduces the impact of electromagnetic interference, improving reliability in industrial environments.

Limitations of Modbus RS-485:

• Complexity in Configuration: Implementing RS-485 networks can be more complex compared to other standards due to the need for proper termination and polarisation of lines.
• Variable Maximum Speeds: Although it offers flexibility in speed, long distances can limit the maximum achievable speed.

What is Modbus TCP/IP (Transmission Control Protocol/Internet Protocol) and how does it work?

Modbus TCP was developed to take advantage of existing LAN network infrastructures, allowing communication over Ethernet networks. It is currently used for any connection between devices that are connected to the internet.

This protocol encapsulates Modbus RTU messages in TCP packets, facilitating their transmission over standard Ethernet networks. One of the main advantages of Modbus TCP is its ability to connect an unlimited number of devices, thanks to the use of IP addresses instead of the addressing limitations of serial protocols.

In this context, Modbus TCP redefines the master-slave relationship in terms of client-server, allowing for more flexible and scalable communication. Devices can act as clients or servers, facilitating the integration of multiple systems and improving communication efficiency in industrial networks.

Here are its features:

• Network Transmission: Data is sent over Ethernet networks, like those you use to connect to the internet.
• Message Format: Messages are encapsulated in TCP/IP packets, which is a standard communication method on networks.
• IP Connections: Each device has a unique IP address, similar to an address in a city.

Advantages:

• Ideal for long distances and large networks.
• Faster communication speeds.
• Easy integration with other networks and systems.

Disadvantages:

• It can be more expensive due to network infrastructure.
• It requires more advanced knowledge to configure and maintain.

What is Modbus ASCII and how does it work?

Modbus ASCII is an older version of the protocol that uses printable ASCII characters to represent data. Although this protocol has largely been replaced by Modbus RTU and TCP, it is still used in specific applications where data readability is a priority. The message structure in Modbus ASCII is similar to that of RTU, but all data is expressed in hexadecimal format, making it easier to manually analyse communications.

What is Modbus plus and how does it work?

Modbus Plus is a high-speed network protocol based on token-bus communication. This protocol is a complete system that includes both the physical and data link layers, allowing for deterministic and highly reliable communication in industrial applications. Modbus Plus uses the RS485 standard for the physical layer and the HDLC protocol for the data link layer, transmitting data at speeds of up to 1 Mbps.

Basic components of the Modbus protocol

Master and Slaves:

• Master: The device that initiates requests and controls communication. For example, a computer that monitors data.
• Slaves: The devices that respond to the master’s requests. They can be sensors, actuators, etc.

Modbus Messages

Data is sent in packets called Modbus messages. These messages contain information about what action to perform and the data needed for that action.

Basic architecture of the Modbus protocol: messages and functioning

The architecture of the Modbus protocol is based on a simple and consistent message structure, regardless of the type of physical interface used. This flexibility allows the same protocol to be used in different types of connections, such as RS232, RS485, or Ethernet. Each Modbus message includes four basic elements: device address, function, data, and error-checking code. This consistency facilitates communication analysis and debugging, improving interoperability between devices from different manufacturers.

How to connect a Modbus network: steps and considerations

To connect a Modbus network, it is essential to consider several factors, including the physical connection, register mapping, and communication parameters. Modbus RTU uses RS485 or RS232 serial connections, while Modbus TCP employs Ethernet networks. It is crucial to obtain the manufacturer’s documentation to understand how registers should be addressed and define the appropriate communication parameters, such as baud rate and slave identification.

Advantages of using Modbus in industrial automation

The Modbus protocol offers numerous advantages in industrial automation applications, including its simple yet effective architecture, ease of integration, and high reliability. The master-slave structure of Modbus RTU allows for efficient communication, while Modbus TCP provides high data speed and almost unlimited connectivity on Ethernet networks. Its simplicity of implementation and lack of licensing costs have contributed to its widespread adoption in the industry.

Limitations and challenges of the Modbus protocol

Despite its numerous advantages, the Modbus protocol also has some limitations. For example, Modbus RTU has limited diagnostic capabilities and requires an independent power supply for devices. Modbus TCP, though more advanced, was designed at a time when data types were less complex, limiting its ability to handle large binary objects and other modern data types. Moreover, the master-slave structure of Modbus can be less efficient in applications requiring simultaneous bidirectional communication.

Integration of Modbus with V2C electric vehicle chargers

The integration of the Modbus protocol into our V2C electric vehicle chargers enables efficient and reliable communication with other devices in the charging system, such as inverters and smart meters.

For instance, the Trydan charging point uses Modbus RTU to operate remotely and obtain data from smart meters, facilitating load management and integration with photovoltaic systems. This advanced communication capability enhances the efficiency and safety of electric vehicle charging systems, ensuring optimal performance and a better user experience.

We recommend you visit our Photovoltaic Integration area for Trydan, where you can find all the devices you can integrate with Trydan. You can now also connect our Pole Pro chargers with Modbus TCP, a solution designed to offer maximum control and efficiency in managing electric charging.

Modbus: an essential tool in the industry of the future

The Modbus protocol is an essential tool in industrial automation, offering efficient and reliable communication between electronic devices. Its adoption in electric vehicle charging applications demonstrates its versatility and ability to enhance the efficiency and safety of charging systems. In summary, Modbus is a popular and effective choice for communication in industrial networks, thanks to its simplicity, flexibility, and high degree of interoperability.