In order that all units with CAN connections are compatible with each other, the general technical data and properties of the CAN buses are set in so-called protocols.

The ISO (International Standardisation Organisation) has declared this protocol a standard and established it in the ISO Standard 11519.

The SAE (Society of Automotive Engineers) has also adopted further standards in view of the special requirements in the area of commercial vehicles.

CAN is originally developed for the automotive industry to replace the complex wiring harness with a two-wire bus.

The specification calls for signaling rates up to 1 Mbps, high immunity to electrical interference, and an ability to self-diagnose and repair data errors.

These features have led to CAN’s popularity in a variety of industries including automotive, marine, medical, manufacturing, and aerospace.

The CAN communications protocol, ISO 11898, describes how information is passed between devices on a network, and conforms to the Open Systems Interconnection (OSI) model that is defined in terms of layers.

Actual communication between devices connected by the physical medium is defined by the physical layer of the model.

The ISO 11898 architecture defines the lowest two layers of the seven layer OSI/ISO model as the data-link layer and physical layer in Figure 1.

Figure 1. The Layered ISO 11898 Standard Architecture

In Figure 1, the application layer establishes the communication link to an upper-level application specific protocol such as the vendor independent CANopen protocol.

This protocol is supported by the international users and manufacturers group, CAN in Automation (CiA).

Additional CAN information is located at the CiA website, can-cia.de. There are many similar emerging protocols dedicated to particular applications like industrial automation or aviation.

Examples of industry-standard CAN-based protocols are KVASER’s CAN Kingdom, Allen-Bradley’s DeviceNet and Honeywell’s Smart Distributed System (SDS).

ISO and Diagnoses for CAN

ISO talks also about error diagnosis functionality for CAN.

If an error arises during the transmission of data through the CAN bus, it can be diagnosed in every vehicle using the so-called "K-line" (ISO 9141).

However, in the future this line should be eliminated and the diagnostic unit connected directly to the defective CAN bus. The ISO already has a recommendation for this which has yet to be adopted.