1. What is CAN Bus?

CAN stands for Controller Area Network, developed by the German company BOSCH, known for its research and production of automotive electronic products, and has ultimately become an international standard (ISO 11898). It is one of the most widely used field buses internationally.

Is CAN Bus a Digital Signal or an Analog Signal?

In North America and Western Europe, the CAN bus protocol has become the standard bus for automotive computer control systems and embedded industrial control local area networks, and it has the J1939 protocol designed specifically for large trucks and heavy machinery vehicles, based on CAN as the underlying protocol.

2. Characteristics of CAN Bus

1. Multi-master operation: Any node on the network can send data to other nodes at any time, making the communication method flexible;

2. Each node on the network has a different priority, meeting real-time requirements;

3. Non-destructive arbitration bus structure: When two nodes transmit information to the network simultaneously, the one with the higher priority transmits first;

4. Three transmission modes: point-to-point, point-to-multipoint, and broadcast;

5. Communication distance can reach 6 km, communication speed can reach 1 MB/s, and the number of nodes can reach 110;

6. Uses a short frame structure, with 8 valid bytes per frame;

7. Has a reliable error detection mechanism, resulting in a very low error rate for data;

8. Automatically retransmits when the sent information is corrupted;

9. Nodes will automatically disconnect from the bus in the event of a severe error to avoid affecting other operations on the bus.

Is CAN Bus a Digital Signal or an Analog Signal?

3. Principles of CAN Bus

The CAN bus sends data from one node to another in a broadcast manner. When a node sends data, the CPU of that node sends the data and the identifier to the CAN chip of the node and puts it into a ready state.

Once the CAN chip receives bus allocation, it transitions to the message sending state, and the CAN chip sends the data in a specified message format.

At this time, all other nodes in the network are in receiving mode, and all nodes must first receive it, determining whether the message is intended for them by detection.

Since the CAN bus uses a content-addressable scheme, it is easy to build control systems that can be flexibly configured, allowing new nodes to be added to the CAN bus without modifying hardware or software.

4. Applications of CAN Bus

The advantages of the CAN bus in networking and communication functions, along with its high cost-performance ratio, determine its broad application prospects and development potential in many fields.

These applications have some commonalities: CAN essentially acts as a bus topology computer local area network in the field. Regardless of the occasion, it handles real-time communication between any nodes, but it has advantages such as simple structure, high speed, anti-interference, reliability, and low cost.

Originally designed for automotive electronic control systems, the application of CAN is now very common in cars produced in Europe. Moreover, this technology has been extended to trains, ships, and other vehicles.

1. Application of CAN bus technology: Well-known foreign cars have adopted CAN bus technology, such as Volvo, Lincoln, Audi, BMW, etc. Domestic car brands, such as Chery, have also applied bus technology in several models. The CAN bus technology sends various driving data of the car to the “bus” through sensors distributed throughout the car body. On this information-sharing platform, any receiving end that needs this data can read the required information from the “bus”, enabling various systems of the car to coordinate, share information, and ensure safe, comfortable, and reliable vehicle operation. Generally, the higher the grade of the car, the more CAN_BUS it is equipped with, and the higher the price, as seen in models like Touran and Passat, which are equipped with multiple CAN buses.

2. Hardware design of automotive CAN bus node ECU: The core technology of automotive CAN bus development involves designing ECUs with CAN interfaces. The CAN bus module of the ECU consists of a CAN controller and a CAN transceiver. The CAN controller executes the complete CAN protocol, completing communication functions, including information buffering and receiving filtering. A CAN transceiver is needed as an interface between the CAN controller and the physical bus, converting the logic level signals between the CAN controller and the bus.

3. Application of CAN bus in domestic independent brand cars: Due to cost control and technological strength, CAN_BUS bus technology generally appears in high-end foreign cars. In A-class and below models, this technology mostly appears in joint venture brands, such as POLO and New Bora. Among domestic brands, there are few models that adopt CAN bus technology, with Fengyun 2 being a representative model. The CAN bus technology of Fengyun 2 enables communication between the engine, transmission, ABS, body, instrument, and other controllers, allowing timely sharing of information throughout the car. In the instrument panel of Fengyun 2, information such as trip mileage, unclosed doors, and seatbelt reminders can all be displayed accurately, doubling the information displayed compared to similar products, thus increasing safety during driving.

5. Is CAN Bus a Digital Signal or an Analog Signal?

CAN bus is a digital signal. Compared with general communication buses, CAN bus data communication has outstanding reliability, real-time performance, and flexibility. Due to its good performance and unique design, CAN bus is increasingly gaining attention.

6. Differences Between Analog Signals and Digital Signals

Analog signals refer to signals whose amplitude values are continuous (amplitude can be represented by an infinite number of values). Continuous analog signals in time include continuously changing images (television, fax) signals, etc. Discrete analog signals in time are a type of sampled signal, which is obtained by sampling an analog signal at intervals of time T. Although its waveform is not continuous in time, its amplitude values are continuous, so it is still an analog signal.

Digital signals refer to signals whose amplitude values are discrete, with values limited to a finite number. Binary code is a type of digital signal. Binary code is less affected by noise and is easy to process with digital circuits, thus gaining widespread application.

The advantages of analog communication are that it is intuitive and easy to implement, but it has two main drawbacks: (1) Poor confidentiality; analog communication, especially microwave and wired clear-line communication, is easily eavesdropped. As long as the analog signal is received, the communication content can be easily obtained. (2) Weak anti-interference ability; during the transmission of electrical signals along the line, they are subject to various noise interferences from the outside and within the communication system. Once noise and signals are mixed, it becomes difficult to separate them, resulting in a decline in communication quality. The longer the line, the more noise accumulates.

Digital communication has the following advantages: (1) Enhanced confidentiality of communication. After voice signals are converted from analog to digital, they can first undergo encryption processing before transmission, and then be decrypted at the receiving end before being converted back to analog signals. (2) Improved anti-interference ability, especially during relay, where digital signals can be regenerated to eliminate noise accumulation. (3) Transmission errors can be controlled, thus improving transmission quality. (4) It is convenient to use modern digital signal processing technology to process digital information. (5) It can construct a comprehensive digital communication network, comprehensively transmitting various messages, thus enhancing the functionality of the communication system. However, digital communication also has drawbacks, such as occupying a wider bandwidth, complex technical requirements, and quantization errors during analog-to-digital conversion.

The messages transmitted by digital communication systems are generally discrete, but they can also be continuous. If it is necessary to transmit analog messages in a digital communication system, the information source at the sending end should include an analog-to-digital conversion device, while the receiver should include a digital-to-analog conversion device. Considering the fact that there are still many analog communication systems, it is often necessary to use them to transmit digital signals. This requires some modifications or the addition of digital terminal equipment.

(Image source from the Internet)

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