Multiplexed Networks for Embedded Systems: CAN, LIN, FlexRay, Safe-by-Wire...

3

The CAN Physical Layer

In the preceding chapters, I described the general principles of the CAN (controller area network) protocol (mainly dealing with OSI/ISO layer 2). As you would certainly have noticed, I have not yet paid much attention to the physical layer along which the CAN frames must travel sooner or later, and its many applications. To fill this gap, I propose to set out a little more of the theory on the physical layer and the problems raised by different types of medium (OSI/ISO layer 1 and layer 0). To make this topic easier to grasp, I have broken down the description into two chapters as follows:

• Chapter 3
  • the physical layer described in the reference document and in the ISO (International Standards Organization) standard,
  • the properties of the bit,
  • the types and structures of networks,
  • the problems of signal propagation, distance and bit rate.
• Chapter 4
  • the different mediums that can be used,
  • the line protection (bus failure management),
  • circuit-to-circuit compatibility,
  • compliance with pollution standards.

3.1 Introduction

At this point in the book, I am assuming that you now have a good knowledge of the protocol, the frame management and all the special features of these systems. All we have to do now is step on the bus while it is moving (a rather dangerous thing to do …!) In short, you know the general structure of the protocol…, but there are still many specific ‘low-level’ questions (in the sense of the OSI/ISO layers, of course) that need to be mentioned ...