In a world rapidly shifting toward smart manufacturing and IoT, a communication protocol is crucial to read and write the message. That’s why Modbus was invented and remains one of the most widely used communication protocols between the old and the new. So simply, what is Modbus? What are the differences among Modbus RTU, ASCII and TCP/IP?
Definition of Modbus
Modbus was introduced in 1979 with the initial purpose of serving as an internal point-to-point communication protocol. Additionally, Modbus is increasingly popular in use of various device type in various equipment vendor thank to its open source features. It is not limited to industrial automation and can be found across a wide range of automation industries.
The Modbus protocol operates on a master/slave architecture. In this model, only the master device can request, while the reverse direction (slaves give requests) is not possible. As a result, the master does not require an address, whereas slave devices are assigned addresses ranging from 1 to 247. Address 0 is implied as a broadcast address to all slaves.
Three types of Modbus communication
Through continuous development, Modbus has become highly flexible and evolved into three main transmission modes: RTU, ASCII, TCP/IP.
Modbus RTU
Modbus RTU (Remote Terminal Unit) is the most widely used variant of the Modbus protocol. It transmits data over RS-232, RS-485, or RS-422.
- RS-232 interface complies with the interface standard for serial data communication established by the Electronic Industries Alliance (EIA). It can communicate via limited distances, one RS232 protocol device per port.
- RS-422 is programmed in the same way, however it can communicate via very long distances, up to 32 devices can be connected per port, better noise immunity than RS232.
- RS-485 can also communicate via very long distances, multiple PC’s and multiple controllers can run on one bus.
While not including a dedicated message header can make it harder to trace specific changes in transaction details, it compensates with a CRC (Cyclic Redundancy Check) mechanism, ensuring effective error detection during data transmission, enhancing communication reliability.
Modbus ASCII
Modbus ASCII (American Standard Code for Information Interchange) uses human-readable characters to format messages, making it easier to read but generally less secure and less efficient than Modbus RTU. In ASCII mode, ASCII characters are used to mark the beginning and end of each message.
It is important to note that Modbus ASCII and RTU are not compatible with each other. A device set to ASCII mode cannot communicate with one using RTU. Additionally, because ASCII messages use more characters, they require roughly twice as many bytes to send the same data compared to RTU.
Brief comparison between Modbus RTU and ASCII:Â
Modbus TCP/IP
Modbus TCP/IP is the Ethernet-based version of the Modbus protocol. It runs over TCP/IP networks and uses the standard TCP/IP stack to handle communication. This version is well-suited for large-scale industrial systems, especially when devices are spread out across different locations.
Brief comparison between RTU and TCP/IP:
Modbus Advantages in Automation Application
Modbus offers several key advantages that make it a popular choice in industrial automation. First, it is simple and easy to implement, which reduces engineering time and cost. Its wide compatibility allows seamless communication between devices, making system integration more flexible and scalable.
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Another major benefit is that Modbus is an open source protocol, meaning it does not require licensing fees to use. Overall, Modbus provides a solid foundation for automation systems that need dependable communication without the complexity or expense of more advanced industrial protocols.
Communication protocol in collaborative environment
In addition to EtherNet/IP, EtherCAT, Profibus, and ProfiNet, Modbus is also a widely adopted communication protocol in the programming of collaborative robots (cobots) and grippers. For instance, Universal Robot, KUKA use Modbus TCP/IP, Omron use both Modbus TCP and RTU,…
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At Apicoo Robotics, the SusGrip 2F and SusGrip 3F smart grippers use Modbus RTU over RS-485, thank to its ease of integration, minimal restrictions, and compact cabling. This makes it ideal for seamless communication in industrial environments.
Additionally, we’re happy to support you in adapting the SusGrip grippers to match your existing communication protocols and standards.
Hope this blog has provided useful insights. If you have any questions or would like to explore how SusGrip can fit into your real-world applications, CONTACT US!
We’re here to help you make the most of your automation needs.
