CAN (Controller Area Network) Bus is a robust and widely used communication protocol in industrial automation, especially in Programmable Logic Controllers (PLCs). As a CAN Bus PLC supplier, I've witnessed firsthand the significance of understanding the common CAN Bus frame formats used in PLCs. In this blog, I'll delve into these formats, their applications, and how they benefit the industrial ecosystem.
Understanding CAN Bus Basics
Before we jump into the frame formats, let's briefly understand what CAN Bus is. CAN Bus is a serial communication protocol that allows microcontrollers and devices to communicate with each other within a vehicle or an industrial environment without a host computer. It was originally developed for the automotive industry but has since found its way into various other sectors, including manufacturing, robotics, and building automation.
CAN Bus operates on a multi - master serial bus, where multiple nodes can send and receive data simultaneously. The protocol uses a message - based communication system, where each message is identified by a unique identifier (ID). This ID determines the priority of the message on the bus, with lower ID values having higher priority.
Common CAN Bus Frame Formats
There are two main types of CAN Bus frame formats: the Standard CAN (CAN 2.0A) and the Extended CAN (CAN 2.0B).
Standard CAN (CAN 2.0A)
The Standard CAN, also known as CAN 2.0A, uses a 11 - bit identifier. This identifier is used to determine the priority of the message on the bus. The frame structure of a Standard CAN message consists of several fields:
- Start of Frame (SOF): A single dominant bit that indicates the beginning of a new message.
- Arbitration Field: This field contains the 11 - bit identifier and a remote transmission request (RTR) bit. The RTR bit is used to distinguish between data frames and remote frames.
- Control Field: It includes the identifier extension bit (IDE), which is always recessive in CAN 2.0A, and the data length code (DLC), which specifies the number of data bytes in the frame (0 - 8 bytes).
- Data Field: This field contains the actual data being transmitted, with a maximum length of 8 bytes.
- Cyclic Redundancy Check (CRC) Field: A 15 - bit CRC code is used to detect errors in the message.
- ACK Slot: The transmitting node sends a recessive bit, and the receiving nodes respond with a dominant bit if they have correctly received the message.
- End of Frame (EOF): A sequence of 7 recessive bits that marks the end of the message.
The simplicity of the 11 - bit identifier in CAN 2.0A makes it suitable for applications where the number of nodes and messages is relatively small. For example, in a small - scale industrial automation system with a limited number of sensors and actuators, CAN 2.0A can provide a cost - effective and efficient communication solution.
Extended CAN (CAN 2.0B)
The Extended CAN, or CAN 2.0B, uses a 29 - bit identifier. This extended identifier provides a much larger address space compared to the Standard CAN, allowing for a greater number of unique messages and nodes on the bus.
The frame structure of an Extended CAN message is similar to that of the Standard CAN, but with some differences in the arbitration field:
- Start of Frame (SOF): Similar to CAN 2.0A, it is a single dominant bit.
- Arbitration Field: It consists of a 11 - bit base identifier, an IDE bit (dominant in CAN 2.0B), a 18 - bit extended identifier, and the RTR bit.
- Control Field: The DLC is used to specify the number of data bytes (0 - 8 bytes).
- Data Field: Can carry up to 8 bytes of data.
- Cyclic Redundancy Check (CRC) Field: A 15 - bit CRC code for error detection.
- ACK Slot: Similar to CAN 2.0A, the transmitting node sends a recessive bit, and the receiving nodes respond with a dominant bit if the message is received correctly.
- End of Frame (EOF): A sequence of 7 recessive bits.
The extended identifier in CAN 2.0B makes it ideal for large - scale industrial automation systems, such as those found in automotive manufacturing plants or large - scale robotic systems, where a large number of devices need to communicate with each other.
CAN FD (Flexible Data Rate)
In addition to the Standard and Extended CAN, there is also the CAN FD (Flexible Data Rate) protocol. CAN FD is an extension of the CAN 2.0 protocol that allows for higher data rates and larger data payloads.
The main differences between CAN FD and the traditional CAN protocols are:
- Data Payload: CAN FD can carry up to 64 bytes of data, compared to the maximum of 8 bytes in CAN 2.0A and CAN 2.0B.
- Data Rate: CAN FD supports a higher data rate in the data field, which can be up to several megabits per second, depending on the implementation.
- Frame Structure: The frame structure of CAN FD is similar to that of CAN 2.0B, but with additional fields to support the higher data rate and larger payload.
CAN FD is well - suited for applications that require high - speed data transfer, such as in advanced driver - assistance systems (ADAS) in the automotive industry or high - performance industrial control systems.
Applications of Different CAN Bus Frame Formats in PLCs
The choice of CAN Bus frame format in PLCs depends on the specific requirements of the application.
Small - Scale Industrial Automation
For small - scale industrial automation systems, such as a local control panel for a single machine or a small production line, the Standard CAN (CAN 2.0A) is often sufficient. Its simplicity and lower cost make it an attractive option. For example, in a simple conveyor belt system, sensors can send status information to a PLC using CAN 2.0A messages, and the PLC can send control commands to the actuators in the same format. You can explore our Compact Mini PLC which can be well - integrated with CAN 2.0A systems.
Large - Scale Industrial Automation
In large - scale industrial automation systems, such as a factory with multiple production lines and a large number of sensors and actuators, the Extended CAN (CAN 2.0B) is more appropriate. The larger address space provided by the 29 - bit identifier allows for a greater number of unique messages and nodes on the bus. For instance, in an automotive assembly plant, different sections of the production line can communicate with each other using CAN 2.0B messages, ensuring efficient and reliable operation.
High - Speed Data Transfer Applications
For applications that require high - speed data transfer, such as real - time monitoring of critical processes or high - performance robotics, CAN FD is the preferred choice. Our EtherCAT Bus PLC can also be integrated with CAN FD systems to provide a comprehensive solution for high - speed data transfer and control.
Benefits of Using CAN Bus in PLCs
Using CAN Bus in PLCs offers several benefits:
- Reliability: CAN Bus uses a differential signaling technique, which makes it resistant to electromagnetic interference (EMI). This is crucial in industrial environments where there are many sources of EMI, such as motors and power supplies.
- Scalability: The CAN Bus protocol allows for easy addition or removal of nodes on the bus, making it suitable for both small - scale and large - scale applications.
- Cost - Effectiveness: CAN Bus is a relatively low - cost communication protocol compared to other industrial communication protocols. It requires less wiring and can be implemented using inexpensive microcontrollers.
- Real - Time Performance: The priority - based arbitration mechanism in CAN Bus ensures that high - priority messages are transmitted first, making it suitable for real - time applications.
Our CAN Bus PLC Solutions
As a CAN Bus PLC supplier, we offer a range of CAN Bus PLC products that support different CAN Bus frame formats. Our PLCs are designed to be reliable, easy to use, and cost - effective, making them suitable for a wide range of industrial applications.
Whether you need a simple CAN 2.0A - based solution for a small - scale project or a high - performance CAN FD - enabled PLC for a large - scale industrial system, we have the right product for you. Our team of experts can also provide technical support and customization services to ensure that our PLCs meet your specific requirements.
Contact Us for Procurement
If you are interested in our CAN Bus PLC products or have any questions about CAN Bus frame formats and their applications in PLCs, we encourage you to contact us for procurement and further discussions. Our experienced sales team will be happy to assist you in finding the best solution for your industrial automation needs.
References
- Bosch, "Controller Area Network (CAN) Specification Version 2.0," 1991.
- ISO 11898 - 1:2015, "Road vehicles — Controller area network (CAN) — Part 1: Data link layer and physical signalling."
- CiA (CAN in Automation), "CANopen — A CAN - based higher - layer protocol for distributed industrial automation," 2019.