The Controller Area Network (CAN) serial bus system originally developed for in-vehicle networking in passenger cars, has been used in embedded machine-control systems since the beginning of the 1990s. Most of those early users developed their own application-layer protocols.
However, the days of data-link layer solutions are over: CAN and Ethernet are the most successful data-link layer protocols. The next challenge is to select a higher-layer protocol.
Around the world, there are several organizations promoting Ethernet-based application layers for industrial applications. None of them has succeeded yet. However, in the CAN world, the battle has been concluded. In factory automation, DeviceNet is the clear winner in its battle with Smart Distributed Systems (SDS), and in embedded machine control, CANopen is the most widely accepted application layer.
With DeviceNet and CANopen, two standardized (EN 50325) application layers are now available, addressing different markets. DeviceNet is optimized for factory automation and CANopen is especially well-suited for embedded networks in all kinds of machine controls. This has made proprietary application layers obsolete; the need to define application-specific application layers is history, except perhaps for some specialized high-volume embedded systems.
Since 1992, the CAN in Automation (CiA) international users and manufacturers group has supported different industries in the development of standardized higher-layer protocols for CAN-based networks. The solution for embedded machine networking has been developed in cooperation with the European Community. The outcome is the CANopen application layer, which has been submitted for European standardization (prEN 50325-4).
In addition to the CANopen application layer, CiA CANopen Special Interest Groups have specified device, interface, and application profiles. The first CANopen users in U.S. include manufacturers of industrial trucks, medical devices (e.g., GE Medical Systems), and several machine builders (e.g., Bell & Howell).
In Europe, CANopen is widely accepted as the higher-layer protocol for embedded machine control in any kind of machinery, including textile machines, injection-molding machines, railways, truck-based superstructures, and even in professional coffee machines. CiA is working very closely with other user organizations in standardizing device profiles, e.g., the Europmap injection-molding machine manufacturers group, the VAK German association of superstructure manufacturers, and VDA German association of public transportation. In addition, the first CANopen practice recommendations have been published by the U.S.-based Industrial Truck Assn. (ITA), and the U.S.-based EPRI user organization has developed the CANopen device profile for battery devices in cooperation with CiA.
But still there are many CAN users in North America specifying their own higher-layer protocols. That's like believing there's a need to define a new human language.
I believe there are enough standardized higher-layer protocols for CAN-based networks to suit any application. For embedded networks using established components (with annual volumes ranging from several hundred to tens of thousands), CANopen seems to be the best solution, in particular, if you want to buy off-the-shelf devices, tools, and protocol stacks.
For system designers, it is very important to reuse application software. This requires not only communication compatibility, but also interoperability and interchangeability of devices. Therefore, CiA supports the efforts of device manufacturers, system designers, and end users to define CANopen device, interface, and application profiles.
In order to provide company and product-independent training and education services, the users and manufacturers group has its own training staff teaching CANopen technology. In addition, CiA provides worldwide consulting services to help users get their CANopen networks up and running.
To make life easier for system designers, there is a CANopen conformance-test tool available. This tool is also used to certify CANopen devices. Even if the tool provides only a static test, up to 80% of failures can be detected.
From my experience, I strongly recommend using only tested devices, regardless of whether they are officially certified or have successfully passed a self-test.
The CiA non-profit organization was founded in 1992. More than 400 companies have become a member, including a number of U.S.-based companies. CiA's activities in North America are still limited, mainly because of the low requirements. In the last few months, however, an increasing number of inquiries have been received, so CiA is planning to establish a U.S. office. In the meantime, U.S. engineers may contact CiA headquarters in Germany by e-mail, fax, or telephone to get the required support.
Holger Zeltwanger is CiA's managing director and also chairman of the ISO Task Force responsible for the CAN standards (ISO 11898). Learn more about CiA's activities at http://www.can-cia.org.
