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Vehicle bus analyzer decodes CAN in symbolic format

Posted: 04 Nov 2005 ?? ?Print Version ?Bookmark and Share

Keywords:lecroy? vba? vehicle bus analyzer? can? controller area network?

New Vehicle Bus Analyzer

oscilloscope maker LeCroy Corp. is actually creating a new testing paradigm with the release of its VBA (Vehicle Bus Analyzer). It's billed by the company as the first oscilloscope that decodes CAN (Controller Area Network) serial data into symbolic (application layer) text.

Significantly, LeCroy's new VBA is based on the company's predecessor waverunner 6000a Series of oscilloscopes and options. In particular, the company's long-memory WaveRunner 6050A and WaveRunner 6100A scopes are the hardware foundation for the VBA.

New capabilities
The VBA adds capabilities to the previously released CANbus TD (trigger, de-code) and CANbus TDM (trigger, de-code, measure/graph) options. LeCroy claims these new adjuncts will make it intuitive for you to understand CAN ECU (engine control units) and vehicle network behavior, and to debug problems.

Using the VBA, you will get to see the range of CAN protocol stack information, symbolic, hex, and electrical signals, with the ability to also view additional in-circuit electrical signals that influence a CAN bus (such as sensor inputs, voltage levels, and transients). You can also use standard and specialized oscilloscope tools to validate and debug your designs. More on this in a moment.

Significantly, up to four different CAN buses can be decoded at one time. LeCroy claims this capability is a breakthrough that will re-define your understanding of ECUs and vehicle bus networks.

The VBA packs a number of additional features, too. For example, it can show complete CAN physical layer and protocol stack information, for the multiple CAN buses. It's also compatible with industry-standard database files. You also get the ability to perform automated timing measurements with statistical and graph views, and you can extract CAN data from a message stream, re-scale it and display and plot decimal values.

In addition, the instrument also lets you do PWM (pulse-width modulated) signal analysis. You get 2-Mpoint/channle memory (optionally up to 24-Mpoints), with 5GS/s sampling on all four channels. The instrument exhibits up a 1GHz bandwidth, too.

CAN symbolic triggering
The VBA also includes an array of CAN and electrical triggering types that can help you isolate events. The CAN triggering previously released in LeCroy's CANbus TD has been extended in the VBA.

Using a DBC database file that contains information pertinent to an operator's CAN messages and signals, you can now symbolically select a specific CAN message (such as ID) or signal (ID and DATA), and then apply a data condition for triggering.

Here's an example: Instead of having to understand to trigger on values such as ID=0x410 and DATA=3f in the second data byte, you can quickly pickfrom a predefined listthe STRSPEED (steering wheel speed of travel) signal that's part of the LWSOUT message, and then define the data condition as desired. Trigger setup is intuitive, requires little or no cross-reference to other files or programs, and results in operator confidence.

Annotation and display
Like CANbus TD and TDM, the VBA color-codes the ID, DATA, DLC (etc.) portions of a signal, and writes the decoded values above the displayed CAN physical layer signal. Compression algorithms are used to keep the display from being too cluttered, while at the same time making error-frame location obvious, even on acquisitions with many hundreds or thousands of messages.

If the CAN message is an Error Frame, the decoding determines the reason for the error frame, saving time.

Industry-standard database
As mentioned above, the VBA uses a standard DBC database file that's commonly used by all automobile makers to define the symbolic/application layer for a specific vehicle's CAN Bus. To use this file, an operator only has to load it onto oscilloscope's hard drive, or onto a memory stick, and recall it from the VBA's user interface; there's no separate pop-up windows or dialog boxes.

The VBA is also a multi-lane software architecture. It can decode up to four different CAN buses simultaneously. In addition, the architecture lets the decoded information be displayed directly on the displayed channel without the need for an intermediate mapped trace.

This makes setup more direct, which LeCroy claims improves system usability. The architecture also provides for future expandability with different serial data-standard decoding algorithms.

Statistical/graphing analysis
The VBA contains specific CAN measurement parameters that allow quick and easy accumulation of statistical information on a wide variety of events. The VBA also contains graphical display tools that permit visualization of the data on your oscilloscope screen. This can be helpful if you're an automotive engineer who needs to statistically prove that pre-defined events are occurring within specified ranges.

You can trigger on defined CAN Bus events, observe actions/reactions, measure timing among CAN and analog signals, or between CAN signals, and view results in a graphical fashion directly on scope's display. Indeed, data on tens of thousands of events can be automatically gathered and analyzed, in a fraction of the time it takes to manually perform the same testing. You can also extract CAN message data from an acquisition and plot the values on the oscilloscope display.

So, for example, you can measure the time a CAN message takes to be transmitted from a low speed CAN bus to a high speed CAN bus through a CAN-CAN gateway. Or, you can measure the time between a wake-up signal and a first complete CAN data frame. Since the wake-up signal is usually a higher-voltage CAN message frame, or a 12-V analog pulse, you could trigger on the higher voltage signal and measure the time to a pre-defined CAN message.

There are more possibilities. You could measure the reaction time from the time an analog signal is input to an ECU, to the time a specific CAN message was generated by the ECU. Or, you could measure the periodic time between identical CAN messages. If, for example, a sensor could be programmed to transmit information to the bus every 100ms, you need to verify that the periodic time between messages is consistent, and within spec.

Visualize analog values
The VBA will let you visualize analog values being transmitted in CAN message format. For instance, steering angle data might be transmitted in CAN message format to a car's ESP (electronic stability) ECU via a CAN steering-angle sensor. This data usually isn't available to be probed and viewed as an electrical signal.

However, viewing the CAN data in an analog format can provide insights into system behavior. In this case, a CAN2Value parameter and a Track function can represent the CAN data on-screen as an electrical signal, just as if it was probed.

PWM measurement
PWM signals are common in a variety of vehicular applications. Fuel injection is usually regulated with a PWM signal, with the width of the signal regulating the amount of fuel injected. In any car, various PWM signals can be present in control circuits, along with CAN signals. It's convenient, therefore, to have toolsets to monitor, measure, and analyze PWM signals.

The JTA2 Jitter and Timing Analysis package included in the VBA permits measurement of pulse width at various levels, and creation of time-correlated tracks of how pulse width changes with time. A lot of engineers working with CAN bus complain that there's no tool that lets them see two buses in a time-correlated way.

Long memory options
The aforementioned WaveRunner 6050A and 6100A oscilloscopes are the VBA's hardware platform. The VBA6050A has 500MHz of bandwidth, a 5GS/s sample rate on all of its four channels, and 2-Mppints/channel of memory (it will interleave to 4-Mpoints on two channels). In many automotive applications, acquisitions can vary from low speed serial data to higher speed signals where transient detection is important.

Likewise, the VBA6100A has 1GHz bandwidth. And, the VBA6100A interleaves both sampling rate and memory to support up to 10GS/s rates with 4-Mppoints/channel when used in a 2-channel mode. As such, you're not getting a specialized CAN scope. You're getting a high-performance general purpose oscilloscope that can be used other of test and debug applications in your lab.

Long-memory options are also available for both the VBA6050A and the VBA6100A. The longest memory option (dubbed the VBA-VL) supports 12-Mpoints/channel using all four channels, or 24-Mppoints/channel using two channels in an interleaved mode.

This capability supports a capture time of 48s for 125kbps and 83.333kbps slow-speed CAN bit rates, and twice that for 33.333kbps CAN bit rates. These capture times are sufficient, in many cases, for periodic message timing calculations.

The longer memory options also provide the ability to increase the sampling resolution and capture time of the acquisition. This can be important when debugging complete vehicle networks.

High-speed transients can be injected onto the CAN Bus and interfere with bus communication. These transients can have significantly faster risetimes than the CAN physical layer signals, and would need to be acquired with a faster oscilloscope sampling rate. Knowledge, and elimination, of unwanted transients can also help you avoid unknown causes of bus communication problems.

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 even days. These waveforms can then be reviewed to determine the cause of unusual bus activity or problems.

Let's say you need 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. The VBA's Sequence Mode permits capture, over a period of hours or days, so you can see all instances of error frames and preceding messages. That can let you understand a repeating pattern on the bus that's causing the error frame to occur.

The 500MHz VBA6050A is priced at about $19,000, and the 1GHz VBA6100A is priced around $24,000.

- Alex Mendelsohn

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