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Using an Oscilloscope for Automotive Serial Bus Testing

Application Notes

Engineers primarily use oscilloscopes to debug and characterize various automotive serial buses. These include the controller area network (CAN), CAN FD, CAN XL, local interconnect network (LIN), FlexRay, single-edge nibble transmission (SENT), and automotive Ethernet. An oscilloscope inherently characterizes the analog quality of these signals. 

 

Performing analog characterization using an oscilloscope is often called physical layer testing. Serial bus protocol analyzers provide optimal measurement performance at the application layer. These instruments provide a trace flow of data at a higher abstract level.

 

This application note explains how to decode, trigger, and symbolically decode your buses. It also includes use-case examples for identifying errors and signal quality issues in your automotive designs. Here’s an overview of what you will learn:

 

Decoding and Triggering on Specific Events

Oscilloscopes display the quality of analog signals. Configuring an oscilloscope to trigger on specific events will bring into focus the details of how buses communicate. Decoding and triggering on common automotive serial control buses is essential for identifying and monitoring the signal quality of specific frames / messages and measuring the timing between frames.

 

Capturing Long Time Spans of Automotive Serial Data 

Sometimes,  it is necessary to capture data from automotive serial buses over long and continuous time spans, such as in power-up sequences. Unfortunately, oscilloscopes have limited amounts of acquisition memory, and that limits the maximum timespan and number of messages / frames that the oscilloscope can capture and decode. Use memory effectively and extend the amount of time that can be captured with segmented memory acquisition. 

 

Using an Eye Diagram for Mask Testing

An eye diagram mask test characterizes the physical layer of automotive serial buses. An oscilloscope eye diagram provides a composite measure of the overall quality of the physical layer in one simple measurement. Keysight InfiniiVision oscilloscopes can perform eye-diagram pass / fail testing on differential CAN and FlexRay buses. 

 

Probing Automotive Serial Buses 

Having a clean connection to your device is important before testing. LIN and SENT represent single-ended signal-to-ground buses. Use standard 10:1 high-impedance passive probes to connect to these signals. Most other serial buses in the automobile, like CAN, CAN FD, CAN XL, and FlexRay, are differential, which means you must measure between two points.

 

Choosing the Right Oscilloscope Platform 

To determine the oscilloscope platform that aligns best with your automotive serial bus or automotive Ethernet measurement needs, consider your oscilloscope performance requirements, such as bandwidth, sample rate, memory, segmented memory, and speed of test, along with your automotive measurement requirements and budget constraints.

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