table of Contents
1. Basic concepts of CAN protocol
The CAN protocol is shown in the following table "ISO/OSI Basic Reference Model", covering the transport layer, data link layer, and physical layer in the OSI basic reference model specified by ISO.
The specific definitions of the transport layer, data link layer and physical layer in the ISO/OSI basic reference model in the CAN protocol are shown in the figure below.
The data link layer is divided into the MAC sublayer and the LLC sublayer. The MAC sublayer is the core part of the CAN protocol. The function of the data link layer is to organize the signals received by the physical layer into meaningful messages and provide transmission control procedures such as transmission error control. Specifically, it is message framing, arbitration, response, error detection or reporting. The functions of the data link layer are usually executed in the hardware of the CAN controller.
The physical layer defines the actual signal transmission mode, bit timing, bit coding mode and synchronization steps. But specifically, the signal level, communication speed, sampling point, electrical characteristics of the driver and bus, and the form of the connector are not defined. These must be determined by the user according to the system requirements.
2. CAN protocol and standard specifications
2.1 ISO standardized CAN protocol
After ISO standardization, the CAN protocol has two types: ISO11898 and ISO11519-2. The ISO11898 and ISO11519-2 standards have the same definition of the data link layer, but the physical layer is different.
- About ISO11898
ISO11898 is a CAN high-speed communication standard with a communication speed of 125kbps-1Mbps.
Currently, ISO11898 has added a new statute to become the new standard of ISO11898-1. - About ISO11519
ISO11519 is a CAN low-speed communication standard with a communication speed of 125kbps or less.
ISO11519-2 is the version of ISO11519-1 with new statutes added.
The following figure shows the scope of the CAN protocol and ISO11898 and ISO11519-2 standards.
2.2 Differences between ISO11898 and ISO11519-2
2.2.1 Differences in the physical layer
As shown in the figure below, the standards of the physical layer in the CAN protocol are different between ISO11898 and ISO11519-2.
The physical layer of the CAN protocol is shown in the figure below. Three sub-layers are defined. The PMA layer and the MDI layer in the physical layer of ISO11898 and ISO11519-2 are different.
In the physical layer (PMA layer, MDI layer), the main differences between ISO11898 and ISO11519-2 are shown in the following table.
2.2.2 The difference of driver IC
The physical layer specifications of ISO11898 and ISO11519-2 are different, and each specification requires a dedicated driver IC to correspond to it. The main driver ICs corresponding to ISO11898 and ISO11519-2 are shown in the table below.
2.3 CAN and standard specifications
Not only ISO, SAE and other organizations, groups, and companies have also standardized the CAN protocol.
Various standard specifications based on CAN are shown in the table below.
As shown in the figure below, the communication protocols for automobiles are classified based on the communication speed.
