Summary of the features of the CAN bus protocol

I believe that you have gained some understanding of this bus protocol through a series of articles on the CAN bus protocol. Now let's summarize this agreement. First, let's take a look at the bit timing requirements of the CAN bus protocol, and then we will analyze the characteristics of the CAN bus protocol.

CAN bus protocol bit timing requirements

The nominal bit rate refers to the number of BITs sent per second by the ideal transmitter without re-synchronization. The reciprocal of the nominal bit rate is the nominal bit time. In different CAN systems, the bit rate of CAN varies. However, in a given CAN system, the bit rate is certain, and its maximum value is affected by factors such as the selected CAN controller type, transceiver, and physical media, it can be set freely within a certain range. The data transmission rate of the CAN bus CAN reach up to 1 Mbit/s. Generally, the Z crystal oscillator is used as the clock generator and the bit timing parameter settings CAN be performed independently, in this way, even if the clock cycles between nodes in the network are different, the same bit rate can still be obtained.

The nominal time can be divided into several non-overlapping time segments, which are synchronous, propagation, phase buffer, and phase buffer.

Analysis of CAN bus features

The CAN bus communication interface integrates the physical layer and data link layer functions of the CAN bus protocol to complete frame-based processing of communication data. One of the biggest features of the CAN bus is the abolition of the traditional station address encoding, instead of coding the communication data block. The ID code of a data frame can be composed of 11 or 29 digits. CAN2.0B specifies that the first seven digits of the identifier cannot be both logical zeros. This is a data frame encoding method, different Nodes can receive the same data at the same time. The maximum data segment length is 8 bytes, which can meet the general requirements for controlling commands, operating states, and test data in the industrial field. At the same time, 8 bytes do not occupy too long bus time, thus ensuring real-time communication. The CAN bus protocol uses CRC and provides corresponding error handling functions to ensure the reliability of data communication. CAN has the following features:

1) CAN works in Multi-master mode, regardless of the master-slave mode. The communication mode is flexible. It uses message identifiers to communicate without site addresses or other node information;

2) node information on CAN is divided into different priorities to meet different real-time requirements;

3) CAN uses non-destructive bus arbitration technology. When multiple nodes send information to the bus at the same time, nodes with lower priority will actively quit sending, the highest priority node can transmit data without being affected, which greatly saves the time for bus conflict arbitration. Especially when the network load is heavy, there will be no network paralysis;

4) You CAN transmit and receive data through point-to-point, one-to-point, and global broadcast through message filtering without the need for special "scheduling ";

5) The maximum direct communication distance of CAN is 10 km;

6) The number of nodes on the CAN depends mainly on the bus driving circuit. Currently, it CAN reach 110 nodes. There are up to 204.8 types of message Identifiers (CAN2.0A), while CAN2.0B's message identifiers are almost unrestricted;

7) the CAN bus protocol adopts a short frame structure, short transmission time, low interference probability, and has excellent error detection effect. Each frame of CAN has CRC and other error detection measures, reducing the probability of data errors. The CAN node automatically disables the output function in case of serious errors, so that operations on other nodes on the bus are not affected;

8) the communication medium of cAN be twisted pair wires, coaxial cables, or optical fiber cables.

CAN bus has been widely used in automotive electronic systems and has become the main industrial standard of European automobile manufacturing industry. It represents the mainstream development trend of Automotive Electronic Control Networks. Modern cars are increasingly controlled by electronic devices, such as scheduled oil injection control of the engine, acceleration, brake control and anti-lock braking system (ABS. Many famous automobile manufacturers in the world, such as Volkswagen, Benz, BMW, Porsche, and Rolls. companies such as Royce and Jaguar have adopted the CAN bus to implement data communication in the internal control system of automobiles.