Complete automotive bus trigger decoding analysis based on Tektronix's new generation portable oscilloscope

CAN FD: To support faster data communication, CAN FD (Flexible Data Rate) was developed, this version has data rates up to 8Mbps and a payload up to 64 bytes.

CAN XL: CAN XL is the latest standard developed by CAN in Automation (CiA), supporting data rates up to 20Mb/s and data field lengths up to 2048 bytes.

Physical layer and data link layer: CAN defines the data link layer of the ISO 7-layer model. The commonly used physical layer specification is ISO 11898. It is a differential 2-wire interface that runs on shielded twisted pair (STP), unshielded On twisted pair (UTP) or ribbon cable.

Communication protocol: CAN uses non-return-to-zero (NRZ) bit encoding and bit stuffing techniques to ensure messages are compact and have high noise immunity. While the bus is idle, any node may start transmitting. CAN and CAN FD use bit-by-bit arbitration when multiple nodes initiate messages at the same time, while CAN XL uses Carrier Sense Multiple Access/Collision Resolution (CSMA/CR) to determine which message has higher priority.

Standards-based: LIN is a low-cost single-wire implementation based on the enhanced ISO9141 standard.

Network structure: The LIN network consists of a master node and one or more slave nodes. All messages are initiated by the master node, and only one slave node responds to each message, so there is no need for conflict detection and arbitration capabilities like CAN.

Communication protocol: Communication is based on UART/SCI, data is sent in the form of 8-bit bytes, with start bits and stop bits, and no parity bits. Data transfer rates range from 1kb/s to 20kb/s, which are slower but suitable for the intended application and help minimize electromagnetic interference (EMI).

Bus status: The LIN bus has two states: active and sleep. When the bus is active, all nodes are awake and listening for relevant bus commands. The bus can be put to sleep by a sleep frame issued by the master node or by bus activity falling below a preset time.

Wake-up mechanism: The bus is woken up by any node requesting wake-up or by an interrupt field issued by the master node.

物理层：FlexRay使用双线差分总线，可以运行在屏蔽双绞线（STP）或非屏蔽双绞线（UTP）上，最高速度可达10Mb/s，显著快于LIN的20kb/s和CAN的1Mb/s。

Dual-channel architecture: An important feature of FlexRay is its dual-channel architecture. This design can provide redundant communication in safety-critical applications to ensure reliable transmission of information; in less safety-critical applications, two channels can be configured In order to transmit different information, the total transmission rate can reach 20Mb/s.

Time-triggered protocol: FlexRay uses a time-triggered protocol, which combines the advantages of previous synchronous and asynchronous protocols. By including static and dynamic frames in the communication cycle, each device on the network is given a fixed-length time slot to communicate.

Frame structure: FlexRay's frame consists of three main parts: header segment, payload segment and tail segment. The header segment includes frame type indicator, frame ID, payload length and other information; the payload segment transmits actual data; the tail segment includes cyclic redundancy check (CRC).

Configuring the input: On a Tektronix oscilloscope, define the oscilloscope's input to a specific bus type (CAN, CAN FD, CAN XL, LIN, or FlexRay) by pressing the "Bus" button on the panel.

Detailed parameter configuration: Inputs include selection of bus standard (e.g. CAN XL), signal type, input channel, bit rate, voltage threshold and sampling point (as a percentage of bit time).

Trigger settings: The oscilloscope offers a variety of triggering options that allow triggering to be configured based on specific bus activity. For example, you can set up to trigger on a specific starting frame, frame type (such as data frame or error frame), specific identifier or data content.

Triggering example: For example, for CAN XL, the trigger can be set to fire at the end of the starting frame or when the frame ID value is a specific number.

Automated Search: Use the Wave Inspector automated search feature to find all bus events that match specific search criteria. This is similar to a trigger setting, but for tagging and browsing events after the data has been fetched.

Search settings: You can set the search for specific starting frames, frame types, priority identifiers, data, error types, etc. to automatically search and mark events that meet these conditions.

Scan the QR code to add "Tektronix Engineer Assistant"

Enjoy 1 to 1 exclusive service now!