Revolutionary development of in-vehicle networking systems

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With the rapid advancement of automotive electrification, in addition to the shift towards battery-driven electric vehicles, traditional vehicles are also beginning to adopt a plethora of electronic systems. These systems deploy a multitude of sensors, processors, and actuators to enhance functionality, safety, and efficiency, leading to a swift increase in the complexity of vehicles. As automotive technology progresses, the demand for In-Vehicle Networking (IVN) systems is also escalating, necessitating higher bandwidth and lower latency communication to ensure functionality and safety. This article will introduce you to the development of in-vehicle networking systems and the relevant solutions introduced by onsemi.

In-vehicle network protocols meet the performance and bandwidth requirements of automobiles

With the development of automotive electronic applications over the years, several primarily (or exclusively) protocols have been developed for in-vehicle networks. Although each protocol has unique attributes, due to the constantly changing architectures and the large amount of data transmitted within in-vehicle networks, these protocols still struggle to meet the demands of today's automobiles. Therefore, automakers are seeking new solutions to provide the necessary performance and bandwidth.

Among various network protocols, Ethernet was once an obvious choice because of its widespread adoption in the computing domain, relatively high bandwidth, and reasonable cost. However, it has a significant drawback when applied to automobiles, which is the inability to operate in a time-sensitive or deterministic mode. This is due to the carrier sense multiple access with collision detection (CSMA/CD) protocol inherent in Ethernet’s operation.

To enable the automotive industry to leverage the advantages of Ethernet, a new protocol has been developed. This automotive-specific protocol variant is known as 10BASE-T1S, which replaces CSMA/CD with Physical Layer Collision Avoidance (PLCA) to achieve deterministic operation essential for drive-by-wire use and Advanced Driver Assistance Systems (ADAS) applications.

Due to its high bandwidth and low latency characteristics, automotive Ethernet is increasingly being used for in-vehicle infotainment systems and ADAS systems. Ethernet plays a crucial role in enabling connectivity features such as Vehicle-to-Vehicle (V2V) and Vehicle-to-Infrastructure (V2I) communication, which are essential for enhancing safety management.

As vehicles rely more on data-driven technologies, the demand for higher bandwidth will continue to grow to support advanced functionalities such as autonomous driving, high-definition/4K video streaming, and augmented reality applications. Ethernet networks in automobiles must provide faster data transmission rates. Future automotive Ethernet networks should also feature ultra-low latency to facilitate rapid decision-making and response for autonomous driving.

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Establish a comprehensive vehicle architecture and imaging solution

For automobile manufacturers, the organization and interconnection of different subsystems within the vehicle interior are important factors to consider. Typically, subsystems are organized based on their functionality (e.g., drivetrain, chassis, comfort) rather than their physical location within the vehicle. This can lead to an increase in cabling complexity, thereby raising the cost and weight of the vehicle.

Recently, the preferred approach is to "zones" subsystems based on their location within the vehicle. Zonal architecture combines scalability and flexibility, allowing relatively easy implementation of changes such as removing, adding, or upgrading subsystems. It also enables deployment of redundant and fault-tolerant elements, which are crucial for achieving the required functional safety level of critical systems.

While the design of zoned architecture reduces the demand for cabling, it significantly increases the volume of data transmitted over the in-vehicle network backbone, requiring higher bandwidth, performance, and low latency. To enable features like Automatic Emergency Braking (AEB) of ADAS, sensors and control electronics are distributed throughout the vehicle, and the reliable operation of safety-critical systems relies on Time-Sensitive Networking (TSN) to eliminate any latency discrepancies.

Undoubtedly, deterministic 10BASE-T1S Ethernet will play a crucial role in future vehicles, especially in the backbone network of a zonal architecture. Protocols like MOST and FlexRay are unlikely to be used in new designs, but LIN and CAN are expected to continue their role, particularly within individual "zones."

Furthermore, there will be continued development of other protocols, including the MIPI Alliance's Camera Serial Interface 2 (CSI-2) and Display Serial Interface 2 (DSI-2), which are essential for connecting high-resolution cameras, sensors, and displays in today's vehicles for ADAS and infotainment systems. Additionally, the MIPI Alliance and the Automotive SerDes Alliance (ASA) are working on standardized SerDes solutions and are focused on enhancing the security of MIPI protocols and enabling asymmetric Ethernet for cameras, involving high-bandwidth transmission and low-bandwidth reception. However, the most significant architectural change is that CAN will no longer be the default protocol for the main vehicle communication backbone; instead, Ethernet will take on this role.

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Basic knowledge of the in-vehicle networking types

In-vehicle networking mainly involves basic knowledge of LIN, CAN (FD), FlexRay, and automotive Ethernet technologies. The following will introduce you to the relevant technical concepts. 

LIN:

LIN adopts a 12V architecture and is based on a single-wire serial communication protocol utilizing the common SCI (UART) byte-word interface. Its maximum speed can reach 20 kb/s (EMC/clock synchronization). The master controls the medium access, responsible for no arbitration or collision management to ensure latency time. It features a clock synchronization mechanism for slave nodes (no need for quartz or ceramic resonator) and allows adding nodes without changing hardware/software in other slave nodes. Typically, it supports fewer than 12 nodes (64 identifiers and relatively lower transmission speeds). 

The Vsup of the LIN physical layer ranges between 7V and 18V. Due to strict requirements for slope and symmetry, the minimum duty cycle is 39.6%, and the maximum is 58.1% (with time constants between 1 µs and 5 µs for bus loads: 1k/1 nF 660/6.8 nF 500/10 nF). The not-synchronized oscillator has a tolerance value of less than 14%.

LIN's communication concept is initiated by the master task (message header), activating the slave task after recognition of identifier to starts message response (1-8 data bytes plus 1 checksum byte). It supports both parity and checksum for data correctness.

CAN:

CAN (Controller Area Network) is another mainstream protocol for vehicle networks. In CAN communication, all devices are equal and can communicate at any time. If a conflict occurs (two devices speaking at the same time), arbitration is used to ensure that messages are understood.

CAN supports asynchronous communication (event-triggered). When the bus is quiet, any node can access the bus. It employs non-destructive arbitration, allowing 100% bandwidth utilization without data loss. Messages with low priority have higher latency, while those with high priority have lower latency. CAN supports variable message priorities based on 11-bit (or extended 29-bit) data packet identifiers, enabling automatic error detection, signaling, and retries. CAN uses twisted-pair cable to communicate with up to 40 devices at speeds of up to 1 Mb/s.

The physical layer of the CAN bus requires termination at both ends of the line. The ISO 11898 standard defines the cable impedance as 120 ± 12 Ω, requiring the use of shielded or unshielded twisted-pair cable. During CAN bus arbitration, if two messages are sent simultaneously through the CAN bus, the bus will use the "logical AND" of the signals. Therefore, the message identifier with the lowest binary number gains the highest priority. Each device listens to the channel and exits if it detects that the bus’s bit does not match its identifier’s bit. CAN supports flexible data rates, and to increase bandwidth, CAN Flexible Data Rate (CAN FD) has been introduced as an extension of CAN. 

Flexary:

The FlexRay protocol, akin to a train-schedule, meticulously schedules all FlexRay traffic using time slots. It boasts high data rates of up to 10 Mb/s and supports time and event-triggered behaviors, redundancy, fault tolerance, and determinism (utilizing "time-slots"). FlexRay meets the error tolerance, speed, and time determinism performance requirements of applications such as drive-by-wire, steer-by-wire, and brake-by-wire.

In the FlexRay physical layer, the static segment is reserved for deterministic data arriving at fixed period, while the dynamic segment is used for more general event-based data that does not require determinism (refer to CAN). Symbol windows are typically used for network maintenance and signaling for starting the network, while network idle time is utilized to maintain known "quiet" times for synchronization between node clocks.

Ethernet:

Ethernet includes standards such as 100Base-T1 and 1000Base-T1, which utilize single twisted-pair cables, support full-duplex communication, and achieve speeds of up to 100/1000 Mbps. Cable lengths can reach at least 15 meters. Differential signals are coupled into the twisted pair cables through capacitors. The physical layer converts bits to symbols (3 bits are converted to 2 symbols), where the symbol values can be +1, 0, or -1, corresponding to three different differential voltage levels. Ethernet supports peer to peer communication, and for more complex networks, switches are required. Communication continues even if no nodes intend to send data to maintain synchronization.

In the case of 100Base-T1, one of the physical layer link partners is Master (initiates training), and the second is Slave (synchronizes its clock with Master using clock recovery from data streams). Since the physical layer employs PAM3 (3 bits converted to 2 symbols), its baud rate is 66 MBd/s, allowing both link partners to transmit symbols simultaneously. As a result, five different differential voltage levels may be observed. Data to be transmitted can be combined with side stream and includes a scrambler (pseudo-random stream) to achieve better EMC performance.

10Base-T1S is a protocol that transmits data at a rate of 10 Mbps over a single twisted-pair cable with length of up to at least 15 meters. It supports peer to peer half-duplex communication. Optional features include full-duplex peer to peer operation and half-duplex multi-point (CAN, FlexRay, LIN, etc.) operation. It can also support multidrop operation with one Master and at least up to 8 Slaves. The Master initiates communication via a beacon, and then each Slave has the opportunity to send data. This protocol is known as Physical Layer Collision Avoidance (PLCA).

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onsemi has been heavily involved in in-vehicle networking with a broad product portfolio

onsemi has been deeply involved in the field of IVN for over 30 years, offering a wide range of products and providing reliable customer support and application support. onsemi's product portfolio covers all mainstream IVN technologies such as LIN, CAN, and FlexRay, while also continuously enhancing its intellectual property (IP) to better meet the requirements and demands of the automotive industry.

With the increasing importance of 10BASE-T1S Ethernet in the automotive industry, onsemi is concentrating most of its development resources on this area. Following the recent release of solutions, onsemi is now developing second-generation products with even higher performance to help the industry continue advancing zonal architecture and autonomous driving technologies.

With over 30 years of supporting the automotive industry and offering a complete portfolio of AEC-qualified products, onsemi enables customers to design high-reliability solutions, create value for end-users, and deliver peak performance. onsemi holds a significant position in the ADAS field, providing a comprehensive product portfolio including power management, lighting solutions, motor drivers, system design expertise, reference designs, powerful and flexible development kits, and experienced application support. Its key components comply with ISO-26262/ASIL standards.

Conclusion

As vehicles become increasingly equipped with electronic systems, the importance of automotive networks is growing rapidly. The automotive networking technologies introduced in this article will be widely used for connecting various automotive electronic systems, providing greater functionality and higher safety standards. With over 30 years of expertise in the automotive electronics field, onsemi can provide comprehensive automotive electronic solutions. For further inquiries or deeper requirements, please feel free to contact onsemi or Arrow Electronics.

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