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Diagnostics in CANopen FD

CAN in Automation (CiA) gives an update on CANopen FD. CANopen FD was published in fall 2017, in order to offer the CANopen users the benefits of CAN FD, in a CANopen environment.

(Photo: CAN in Automation)

CANopen FD offers the user not only to overcome payload limitations by means of 64-Byte PDOs, it enhances CANopen FD with a very flexible universal service data object (USDO), as well. The USDO meets the requirements of modern control systems that may be modified by the end user and where cross-communication between the devices needs to be established during system runtime, by absence of system designer. The enhanced EMCY write service provides comprehensive diagnostic information that allows quick trouble shooting and reduces therefore system down times. Except of these helpful amendments, most of the well-known CANopen functions are kept. Todays CANopen users can re-use their CANopen experiences to maintain CANopen FD systems.

CANopen FD lower layer setup

CANopen FD makes use of the CAN FD data link layer and physical layer. To avoid troubles in a CANopen FD system it is important to setup the lower layer design very carefully. To assist device and system designers, CAN in Automation maintains the CiA 601 specification series, which provides useful implementation hints. E.g. for fast data phase bitrates, the bit time gets very short.

The error state indicator (ESI) provides the CAN error state of the CAN frame producer (Photo: CAN in Automation)

New Signal Improvement Circuitry (SIC) transceivers, as introduced in CiA 601-4, should be considered to allow high data bit rates and stable voltage levels even in non-linear bus topologies. To assess the status of a CANopen FD system on data link layer level, CAN FD provides the Error State Indicator (ESI) Bit. The ESI Bit indicates the CAN error state of the producer of a CAN frame. Therefore by evaluating the ESI bits of all communicated CAN frames, system maintainers get the information, how many network participants are in trouble.

Means for diagnostic in CANopen FD

The data object 1001h – already known from classic CANopen – provides a good base for the start of diagnostics. With one simple USDO read access in broadcast, the system designer gets the information, which CANopen FD device is currently in an error situation. For more detailed diagnostics, the new data object 1031h provides all the error events that have been occurred in the CANopen FD device. These error events are stored to sub-index 04h, coded as DOMAIN. Single error events are coded in the same way as the related EMCY write protocol. The CANopen FD EMCY write protocol provides a time stamp, indicating when the error occurred, the severity of the error, and in which part of a complex device an error occurred. Even an NMT reset command does not influence the content stored to this data object. Only dedicated control commands can influence the content of this error history.

The error history domain data is filled during independently of the life time of the CANopen FD communication interface. An active CANopen communication interface just enables access to the error history domain data via the CANopen FD communication services. The size of the error history domain depends on the CANopen FD device’s available resources in its internal RAM area. The system maintainer can read the number of recorded error events in sub-index 01h. The type of recording error events, can be adjusted via sub-index 02h Error history command. This allows storing of only relevant errors; e.g. errors of a specific priority, or to assure that no events are overwritten, in case the active error history is filled up.

Due to the broadcast communication in a real bus-line architecture, a data-logger would record all error events, communicated by EMCY write protocols. This way system designer’s can benefit from the enhanced error information. Using a common time base in a system allows bringing all error events of a system in the chronological order; thanks to the new time stamp. To get an quick overview on the currently active errors, a CANopen FD device provides the active error list in data object 1032h. In contrast to the DOMAIN in data object 1031h, this object displays just devices errors that are currently present at the device and they are removed from the list, if they are solved.

CAN FD and CANopen FD seminars

In June, CAN in Automation will offer seminars about CAN FD and CANopen FD.

The CAN FD seminar on 04 June 2019 focuses on the improved CAN FD protocol, as specified in ISO 11898- 1:2015. Attendees learn the details of the CAN FD protocols and the differences to Classical CAN. Additionally, the seminar discusses further relevant aspects with regard to CAN FD device design, system design, as well as diagnostics. Furthermore it gives an overview on the impacts of CAN FD on CAN-based higher layer protocols.

The CANopen FD seminar on 05 June 2019 explains in detail the CANopen FD protocol as specified in CiA 1301. Attendees get familiar with the embedded network design options provided by CANopen FD. Additionally, it provides know-how about that most of already available classic CANopen knowledge is applicable in CANopen FD networking, as well.

CiA members can attend the seminars free-of-charge.


CAN FD is already in use by commercially available passenger cars and CAN hardware is available in various formats. CANopen has been updated with regard to CAN FD and can support system designers in their tasks to setup modern CAN-based systems that meet the requirements of todays and tomorrows embedded networking. This covers also means for diagnostics and trouble shooting.

Detailed evaluations of the CAN FD physical layer require typically tools that allow an analysis of the bit timing, termination of the system or the signal quality. The CAN FD protocol provides already an Error State Indicated (ESI-bit) that serves as first indicator for the quality of the CANopen FD system. In CANopen FD, the enhanced error handling, implemented in an Active error history, the updated EMCY write protocol and some well-known features for diagnostics, derived from CANopen, support system designers to keep the runtime of their CANopen FD based system high. First CANopen FD devices were exhibited at CiA’s booth on occasion of Embedded World 2019.


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CAN in Automation