Engineering Autonomous Vehicles and Robots. Shaoshan Liu

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Engineering Autonomous Vehicles and Robots - Shaoshan Liu


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      2.1 Introduction

      In this chapter, we introduce in-vehicle communication systems. We first introduce CAN bus, which is a high-integrity serial bus system for networking intelligent devices. Also, we introduce FlexRay, a deterministic, fault-tolerant, and high-speed bus system developed in conjunction with automobile manufacturers and leading suppliers; FlexRay is meant to gradually replace CAN as the default in-vehicle communication network. In addition, we introduce CANopen, a communication protocol and device profile specification for embedded systems used in automation, as well as CANopenNode, a free and open source CANopen Stack written in ANSI C in an object-oriented way. We believe this chapter will provide sufficient background for readers to understand in-vehicle communication networks.

      A CAN bus is a high-integrity serial bus system for networking intelligent devices. CAN buses and devices are common components in automotive and industrial systems. Using a CAN interface device, applications can be developed to communicate with a CAN network [1,2].

      In the past few decades, the need for improvements in automotive technology caused increased usage of electronic control systems for functions such as engine timing, anti-lock brake systems, and distributor-less ignition. Originally, point-to-point wiring systems connected electronic devices in vehicles. As more and more electronics in vehicles resulted in bulky wire harnesses that were heavy and expensive, point-to-point wiring was no longer scalable.

      To eliminate point-to-point wiring, automotive manufacturers replaced dedicated wiring with in-vehicle networks, which reduced wiring cost, complexity, and weight. In 1985, Bosch developed the CAN, which has emerged as the standard in-vehicle network.

Image described by caption and surrounding text.

      As CAN implementations increased in the automotive industry, CAN (high speed) was standardized internationally as ISO 11898. Later, low-speed CAN was introduced for car body electronics. Finally, single-wire CAN was introduced for some body and comfort devices. Major semiconductor manufacturers, such as Intel, Motorola, and Philips, developed CAN chips. By the mid-1990s, CAN was the basis of many industrial device networking protocols, including DeviceNet and CANOpen.

      If it is not, the station assumes that a higher priority message is being sent and, therefore, halts transmission and reverts to receiving mode. The highest priority message gets through and the lower priority messages are resent at another time. The advantage of this approach is that collisions on the network do not destroy data and eventually all stations gain access to the network. The problem with this approach is that the arbitration is done on a bit-by-bit basis requiring all stations to hear one another within a bit time (actually less than a bit time).

Diagram depicting CAN protocol layers for ISO data link, physical, and media from top to bottom: Application Layer; Logical Link Control (LLC); Media Access Control (MAC); Physical Layer Signaling (PLS); Medium Attachment Unit (MAU); Transmission Media.
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