LIN, CAN and FlexRay Serial Bus Debugging with Oscilloscopes

　　In order to improve system communication efficiency and reduce costs, all current automotive designs use a large number of serial bus communication protocols. I2C and SPI protocols are commonly used in chip-to-chip communication of electronic control units (ECUs). For long-distance serial communication and control between various automotive subsystems (such as comfort control systems, anti-theft locks, transmission systems, and engine controls), CAN, LIN, and FlexRay protocols are the most common serial bus applications in today's automotive industry.

　　The LIN serial bus based on a master-slave relationship is mainly used in applications that do not require high safety, such as seat and window control. The CAN serial bus uses differential event triggering, which has higher noise immunity than the single-ended LIN bus and has been used as the main control bus for automobiles for more than 20 years. The FlexRay serial bus uses differential time triggering and synchronous deterministic schedules. As an emerging serial bus technology, FlexRay is used in some high-end automobiles and is mainly suitable for systems with high performance and safety requirements.

　　However, serial bus communications are often subject to signal integrity issues caused by the non-ideal environment inside the car, including signal interference from the ignition system and random system noise, which can sometimes cause errors in critical communication cycles. Although serial bus protocol analyzers are great for testing and monitoring the transmission of serial bus data at higher-level protocol and application layers, they cannot measure the integrity/quality of your car's serial bus signal (physical layer).

　　Some current mid- to high-performance digital storage oscilloscopes (DSOs) offer LIN, CAN, and FlexRay bus decoding and triggering capabilities, which can establish a time-correlated link between the protocol layer and the physical layer.

　　Figure 1 shows an Agilent 3000 X-Series oscilloscope simultaneously capturing and decoding CAN and FlexRay buses. At the bottom of the display are time-correlated decode traces for each bus, below the captured physical layer waveforms. The top half of the oscilloscope display shows the industry's only time-interleaved "lister" display, sometimes called an event table. This data format is closer to that of a traditional protocol analyzer.