In order to enhance system communication efficiency and reduce costs, modern automotive designs rely heavily on serial bus communication protocols. I2C and SPI are commonly used for short-range, inter-chip communication within electronic control units (ECUs). For longer-distance communication between various vehicle subsystems—such as comfort systems, anti-theft mechanisms, transmissions, and engine controls—CAN, LIN, and FlexRay are the most widely adopted protocols in the automotive industry.
LIN buses, which operate on a master-slave architecture, are typically used in non-critical applications like seat and window control. In contrast, CAN buses use differential signaling with event-triggered communication, offering better noise immunity compared to the single-ended LIN protocol. CAN has been the dominant control bus in vehicles for over two decades due to its reliability and performance. FlexRay, an emerging technology, uses differential time-triggered communication along with a deterministic schedule. It is primarily found in high-end vehicles where high performance and safety are critical.
Despite their advantages, serial bus communications can suffer from signal integrity issues caused by the complex and noisy environment inside a vehicle. Factors such as interference from the ignition system or random electrical noise can lead to errors during critical communication cycles. While Serial Bus Protocol Analyzers are effective at monitoring data transmission at higher protocol and application layers, they cannot assess the physical layer quality of the serial bus signals.
To address this gap, some mid-to-high-end digital storage oscilloscopes (DSOs) now offer decoding and triggering capabilities for LIN, CAN, and FlexRay buses. These tools allow engineers to correlate protocol-layer data with the actual physical signals, providing deeper insights into communication behavior.
Figure 1 illustrates the Agilent 3000 X-Series oscilloscope capturing and decoding both CAN and FlexRay buses simultaneously. At the bottom of the display, you can see time-correlated decoding traces for each bus, positioned beneath the corresponding physical layer waveform. The top portion of the screen features the industry's only "list" or event table display, which resembles traditional protocol analyzers and helps users interpret communication events more effectively.
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