Chestnut Ridge, New YorkTest-and-measurement vendor LeCroy is now offering a CAN Bus (Controller Area Network) test adjunct for its existing long-memory WaveRunner 6000A Series of oscilloscopes (a WaveRunner 6050A model, for example, has 500-MHz bandwidth, a 5-Gsample/s sample rate on four channels, and one million points of memory per channel).
A word about the automotive-oriented CAN bus. It's a balanced (differential) 2-wire interface running over either shielded twisted pair cabling, un-shielded twisted pair, or ribbon cable. Each node in a CAN network uses a 9-pin D-type connector to connect to the bus. Bit encoding is NRZ (non-return to zero) with bit-stuffing. The use of NRZ ensures compact messages with a minimum number of transitions, as well as resilience to disturbances.
LeCroy's got two new accessories for CAN Bus test, dubbed CANbus TD and CANbus TDM. These adjuncts, along with a WaveRunner scope, can help you locate CAN Bus PHY (physical layer) problems. These products can also aid debugging CAN Bus controllers and systems.
In use, a system equipped with these accessories lets you correlate PHY layer signals with protocol layer data information. According to LeCroy, having all of this information in one place will let you intuitively find problems that you may not have been aware of. Of course, this kind of testing can also increase parts and systems reliability, and help lower costs.
CANbus TD, priced at less than $2200, combines LeCroy oscilloscope capabilities, CAN Bus triggering, and protocol decode. The system lets you capture a specific CAN message or error frame and view protocol data, on the same display as CAN analog signals.
Click for larger typical scope screen image
For its part, CANbus TDM adds measurement and graphing capability to the CANbus TD's triggering and decoding capability. CANbus TDM costs about $3800.
The flexible CAN Bus trigger also lets you trigger in multiple formats (hexadecimal, binary, or even decimal) for a variety of set-up conditions. This can eliminate the need to search through a long capture for the right CAN message.
Instead, you'd trigger on it, then view the CAN analog signal, and then view other signals (such as analog sensor signals). You verify system performance with standard oscilloscope tools.
Or, you can determine sources of bus errors by triggering on just Error Frames, and then directly viewing the CAN error frame analog signal. LeCroy claims this gives you an intuitive understanding of underlying problems on the bus.
CANBus TD also provides a protocol decoding algorithm. It decodes a CAN message into hex or decimal data, and color-codes the ID, DATA, DLC, etc. portions of the signal. If the CAN message is an Error Frame, the decoding determines the reason for the frame, saving time.
CANbus TDM also adds measurement graphing capability to CANbus TD's trigger and decode capability. CANbus TDM contains specific CAN measurement parameters that permit accumulation of statistical information on a variety of events. It also contains graphical display tools that support visualization of the data on your oscilloscope screen.
For example, you can trigger on defined CAN Bus events, observe actions/reactions, measure timing among CAN and analog signals, and view results in a graphical fashion directly on your scope's display. There's no export of data required.
Data on tens of thousands of events can be automatically and quickly gathered, and analyzed, in a fraction of the time it takes to manually perform the same testing. Or, you can extract CAN message data from an acquisition and plot the value as a re-scaled decimal value in user-defined units. LeCroy contends TDM is the missing link toolset between CAN triggering and CAN timing and message data evaluation.
Long Memory's Advantage
Long memory in the associated 6000A scope permits capture of several seconds of CAN Bus traffic and analog signals with high resolution. You can then zoom in on specific areas of interest.
Long memory can also be used with a Sequence Mode to capture thousands of waveforms that meet a specified trigger condition, and that occur over a period of hours or days. These waveforms can then be reviewed to determine the cause of unusual bus problems.
For example, say you'd like to understand the cause of error frames in your system. In realtime mode, you could trigger on error frames and capture the next error frame, and twenty CAN messages that preceded it.
Likewise, in Sequence Mode you could capture--- over a period of hours or days---all instances of error frames and preceding messages. That can help you understand a repeating pattern on the bus that causes an error frame to occur.
For more info, contact LeCroy Corp., LeCroy Customer Care Center, 700 Chestnut Ridge Rd., Chestnut Ridge, New York 10977. Phone: 800-453-2769 or 845-425-2000. Fax: 845-425-8967. E-mail: firstname.lastname@example.org.
Click here for a CANbus TD datasheet (in Adobe Acrobat .PDF format).
Click here for a CANbus TDM datasheet.
Be sure to check out LeCroy's Web site, too.