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

8

Think ‘Bus’, Think ‘Fail-safe SBC’, ‘Gateways’ …

I have now briefly described a large number of ‘serial’ communication systems. In the previous chapters, you would no doubt have noticed that each system has its own characteristics which make it preferable for certain proposed applications (protocol power, cost, dedicated functionality, etc.).

In an industrial, motor vehicle or aeronautical project, many of these applications are present and coexist in the final system. Moreover, some messages in any communication system must, for many reasons, be carried on another system as well. For example, the engine rpm (at high speed) must be displayable on the dashboard (at lower speed). We therefore need to design gateways and repeaters between networks and buses (see Figure 8.1) for various transfers:

• from one speed to another, for example
  • from high-speed CAN (controller area network) 1 to high-speed CAN 2;
  • from low-speed fault-tolerant CAN to high-speed CAN;
• from one medium to another, for example
  • from one-wire CAN to differential pair CAN;
  • from differential pair CAN to optical fibre CAN;
• from one bus to another, for example
  • from CAN xxx to LIN (local interconnect network),
  • from CAN xxx to D2B or MOST or IEEE/IDB 1394;
• etc.

Very commonly, a minor or major operation is also performed on the transferred message as it passes through the gateway; this may involve a change or readdressing of the destination address(es), calculations using the message content, etc. This tends to occupy ...