Oscilloscope Measurement Tools to Debug Automotive Serial Buses Quickly

Using the HD3 Series Oscilloscope

Many oscilloscopes on the market offer automotive-focused options. However, Keysight’s InfiniiVision HD3 Series oscilloscopes offer unique hardware-based measurement capabilities for debugging and characterising the physical layer of automotive serial buses.

This application note explores the unique automotive measurement capabilities and advanced analysis features on InfiniiVision X-Series oscilloscopes to help you quickly debug and characterise the physical layer of automotive serial buses.

Those capabilities include the following:

• Hardware-based decoding for responsiveness
• Dual-bus time-interleaved lister display
• Decoding of all frames captured using segmented memory
• Zone trigger to isolate occurrences of CAN bus arbitration

Figure 1. The InfiniiVision HD3 Series is the ONLY oscilloscope in this class that offers hardware-based serial decoding.

Fast Oscilloscope Waveform Update Rate

The HD3 Series oscilloscopes can update over 1.3 million waveforms per second with Keysight’s exclusive custom ASIC technology. HD3 oscilloscopes remain responsive even when capturing long waveforms while using automatic deep acquisition memory (100 Mpts per channel), which automotive serial bus applications often require. Figure 2 shows that a responsive scope enhances the usability of the instrument, as well as its probability of capturing elusive events that may be problematic in automotive designs.

Waveform update rates can be extremely slow when using deep memory on other vendor’s oscilloscopes. Not only does this make the scope difficult to use, but it decreases the probability of finding an infrequent glitch.

Figure 2. An update rate of 1.3 million waveforms per second easily captures infrequent glitches and jitter.

Hardware-Based Decoding

HD3 Series oscilloscopes are the only oscilloscopes on the market that use hardware-based decoding of CAN, CAN FD, LIN, and all other supported serial buses. Hardware-based decoding provides a real-time update of the decode trace.

This capability enhances the scope’s probability of capturing and displaying infrequent serial bus communication errors, such as error frames and form, acknowledge, CRC, and stuff bit errors, as shown in Figure 3.

Figure 3. Hardware-based decoding captures and displays an infrequent CAN stuff bit error followed by an error frame.

Dual-Bus Time-Interleaved Protocol Lister Display

Most oscilloscopes with serial bus options can display decoded data in two formats. One format shows one or more decode traces time-correlated to the captured waveform. This decode trace is useful when the scope’s time base is set up to view a single frame. The time-correlated decode trace appears near the bottom of the scope’s display (below the waveforms) on HD3 Series oscilloscopes. The second decode format is what Keysight calls the “lister” display. The lister display shows a tabular list of decoded data with column labels based on the fields for the specific protocol.

Automobiles use multiple buses for control and monitoring, including the CAN, CAN FD, LIN, and other buses. Data sometimes needs to pass from one bus to another. Automotive vendors use chips known as “gateways” to interchange data between buses. InfiniiVision HD3 Series oscilloscopes can display time-interleaved decoded data from two buses in the same lister table, as shown in Figure 4. The LIN bus frames are green, and the CAN bus frames are blue in this example. The time-interleaved lister display makes it easy to trace data that passes from one bus to another.

Figure 4. Dual-bus time-interleaved lister display makes it easier to track data through CAN-to-LIN gateways

Segmented Memory Acquisition with Frame Decoding in a Lister Display

Automotive engineers often need to capture multiple and consecutive — yet selective — frames of serial data. For example, they may want to capture each consecutive occurrence of errors without capturing everything in between. Without segmented memory acquisition, the alternative is to use a scope with extremely deep memory and then wade through all that memory after capturing a long record that includes all frames (not just selective frames). This process can take a long time.

Engineers can set up the HD3 Series oscilloscopes to capture segments with precise time-tagging between each frame. Then they can review them individually with automatic decoding (time-correlated decode trace and lister). This makes it easier to measure the time between occurrences of a particular error. It also allows engineers to track the sensor output data each time the error is transmitted, as shown in Figure 5.

Figure 5. Segmented memory acquisition with automatic decoding selectively captures CAN packets with precise time-tagging between each occurrence

Use Zone Triggering to Isolate and Characterise CAN Bus Arbitration

Identifying when CAN bus arbitration is occurring is easy if the oscilloscope’s waveform update rate is fast. Triggering on occurrences of arbitration based on specific CAN messages is not so easy with most scopes.

But the InfiniiVision oscilloscope’s zone trigger capability lets you establish a “zone” where arbitration occurs (first few bits of each frame) while also qualifying the trigger condition on a specific frame ID (or symbolic message name), as shown in Figure 6. You can then use the oscilloscope’s segmented memory acquisition to capture consecutive occurrences of arbitration to characterise how often it occurs.

Figure 6. Characterisation CAN bus arbitration using the oscilloscope’s zone triggering capability

More HD3 Resources

Application Notes, eBooks & White papers:

• Webinar: Debug Designs with the New HD3 Oscilloscope
• Keysight InfiniiVision HD3 Series Oscilloscope
• Fact Sheet: Keysight InfiniiVison HD3 Series
• Datasheet: Keysight InfiiVision HD3 Series
• White Paper: Journey of a Signal White Paper