Keysight HD3 Series Tools to Debug Automotive Serial Buses | APC
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Oscilloscope Measurement Tools to Debug Automotive Serial Buses Quickly

Using the HD3 Series Oscilloscope

An oscilloscope has an inherent ability to characterise the analogue quality of automotive serial buses such as CAN, CAN FD, LIN and so many more. That is why engineers often use oscilloscopes to debug and characterise these signals. Performing analogue characterisation using an oscilloscope is known as taking physical-layer measurements. When analysing the physical layer, it is critical the oscilloscope is still operating at its fastest speeds so you can see any infrequent errors on your buses that could cause serious defects. You can only see these infrequent errors if your oscilloscope is doing serial decoding in hardware. Software decoding causes an oscilloscope to run too slowly to catch any rare events.

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
Keysight HD304MSOKeysight HD304MSO

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.

Keysight HD3 Fast Oscilloscope Waveform Update RateKeysight HD3 Fast Oscilloscope Waveform Update Rate

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.

Keysight HD3 Hardware-Based DecodingKeysight HD3 Hardware-Based Decoding

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.

Keysight HD3 Dual-Bus Time-Interleaved Protocol Lister DisplayKeysight HD3 Dual-Bus Time-Interleaved Protocol Lister Display

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.

Keysight HD3 Segmented Memory Acquisition with Frame Decoding in a Lister DisplayKeysight HD3 Segmented Memory Acquisition with Frame Decoding in a Lister Display

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

Segmented memory acquisition in the HD3 Series oscilloscopes automatically decodes frames. HD3 oscilloscopes are the only scopes that display all decoded frames from segmented acquisitions in the protocol lister display.

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.

Keysight HD3 Use Zone Triggering to Isolate and Characterise CAN Bus ArbitrationKeysight HD3 Use Zone Triggering to Isolate and Characterise CAN Bus Arbitration

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

All of today’s major oscilloscope vendors offer options for triggering on, decoding, and searching data on the CAN, LIN, CAN FD, and all other major serial buses. However, only the Keysight HD3 Series offers hardware-based decoding to ensure you don’t miss any rare events that can cause defects in your design. This combined with the other unique capabilities of Keysight’s HD3 scopes, like the lister display, will help you characterise and debug the physical layer of automotive serial buses fastest with the most accuracy.

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When it comes to providing affordable, yet immensely valuable electronic test equipment to fulfil your high-power testing requirements, APC’s team of test and measurement experts undertake regular training in Keysight products and their applications. Our field-based sales team provide both in-house and remote product demonstrations, advice on selecting the right Keysight product to meet your exact test requirement and technical guidance on how to get the most from your equipment.

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