CAN Newsletter March 2006

Develop CANopen devices the easy but safe way

This article describes how a CANopen device can be developed successfully in shortest time and highest quality with the aid of software tools.
CANopen has gained a lot of momentum throughout the last years: More and more devices are equipped with CANopen protocol interfaces. As last year’s sales figures are showing, the number of CANopen implementations is still increasing. New application fields have just started to show an effect on sales figures and will be increasing still. Thus also an increased demand can be observed for tools that speed up the development process without the hassle of studying a large (and increasing) number of CiA documents.
Modern development processes require not only the availability of some code - either delivered as source code, binary library, DLL or other - but is has become necessary to support device development in all phases, from specification to testing.
The following considerations play a decisive role:

• How to get to the fastest and most cost effective implementation in conformity with the CANopen standard?
• How is the implementation carried out?
• Which software tools are available? Do they cover the complete development life cycle?
• Which of these are actually useful?

CiA has published standards for the communication in a CANopen network. The CANopen services available are defined in the communication profile CiA 301, CiA 302 or other CiA 3xx profiles. Special device functions with their parameters are defined in device profiles. More than 20 device profile standards are currently available.
A CANopen drive can be divided into following parts:

• Device application, device-profile specific, handling process I/O
• Object dictionary, communication and device profile part
• CANopen communication stack
• CAN driver interface

CANopen diagnose and micro-controller debugging

For verification of micro-controller software and for diagnosis of CAN to date usually two different tools are used featuring two separate communication devices for CAN and debug interface to the micro-controller – running often on two separate PCs. A solution for this dilemma is the integration of a CAN recorder in the micro-controller debugger including a flexible message formatting mechanism for CANopen and other protocols. This approach allows a significant increase of efficiency compared to traditional solutions based on separated tools.
Since only layer 1 and 2 of the OSI reference model are defined as transport media in the underlying CAN bus it is necessary to use an application layer protocol (layer 7) to describe the data exchange. For this CANopen is a widely used standard (EN 50325-4). A CAN message is structured at the lower layers via an identifier and up to 64 bits of data. A standard identifier (CAN base frame) contains 11 bits and an extended identifier (CAN extended frame) 29 bits. So single bus nodes respectively bus node functions are addressable respectively observable. The content of the message is included in the 64 bits of data.
The importance of the single message ID for the standard identifier range (0-7FFh) is defined in CANopen. Necessary for the transport of data are the service data objects (SDO) and process data objects (PDO). Whereas the SDOs are designed reading and writing of configuration and status data, the PDOs are used for the actual application data. The CANopen standard provides a scheme for using the program data objects via so called device profiles.

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Automotive portable measuring system

Interaction failures of nodes are the main difficulty during the testing of vehicles or other complex networks of individual units. The causes are hard to detect since errors are not always reproduceable. FeliCase (www.felic.net) was developed to find a remedy for such problems. The tool records telegrams between the components at the as ambient conditions, e.g. voltage, currents, temperatures, contents of headunits, audio signals/dictated notes, video recordings of traffic events and driver activities. All values and events are converted into CAN messages and recorded along a common time base with a data logger. Evaluation software presents the recorded data on a time bar comparable to a video editing software. The tool can be compared to an airplane black box that helps to determine the causes of a failure. FeliCase automotive was awarded a price for product innovation in 2005 by the ISB Mainz (Investitions- und Strukturbank Rheinland-Pfalz).

Measurement case

A battery-backed electric power supply with power management is included in the scope of delivery. The advantage of this is that the measurement can be done without burdening the on-board car power-supply and also to measure at temperatures below 0 °C. A hand-held unit that is connected to a cable works as a remote control for the driver. An additional wireless LAN remote control for notebooks is also available, although the box has a fully integrated personal computer (Windows XP) inside to run measurement software. The case can be remotely controlled with a provided ActiveX. Other programs on the personal computer can be likewise controlled by the hand-held unit. Also available are hardware and software solutions that detect freely definable combinations of CAN messages and perform actions thereupon. The measuring modules can be assigned to the five recording channels of the data logger by the use of the integrated CAN-patch panel. Vehicle CAN lines or outputs of external devices can be connected in the same way.

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