Control Area Network, CAN Standard for serial data communication. Differential transmission on a twisted pair wire. ISO11992 & J1939 (differs in data transfer rate and voltage levels)
CAN message format Three major parts: ID, DLC, and data. CAN messages contains no dest. address. Source address is encapsulated in the ID. 8 bytes of data per message (max).
CAN gateways and the ID field A CAN gateway changes the source ID to one that represents the vehicle from which it originated. Cyclic message informs about location.
Project goal / problem statement How to extend the CAN-bus into the trailer's ? Which wireless technology to use ? How to combine the chosen wireless technology & the CAN protocol ? Wireless link nodes CAN - SAE J1939 CAN - ISO 11992 or SAE J1939 Handheld Computer ?
Problem Statement A wireless gateway that can be placed anywhere in a road train. Should be “stand alone”. Possible a serial link in parallel to CAN
DECT & BlueTooth They are both wireless technologies supporting data and voice transfer. European standards Data transfer rates ~300 – 700 kbps Built to deal with interference
DECT BlueTooth 1880 –1900 Mhz 2.45Mhz in North America. Data transfer rate: 552kb/s in one direction or 288kb/s bidirectional 2.45Mhz Spain, France, and Japan have narrower bandwidth. Data transfer rate: 723kb/s in one direction or 433kb/s bidirectional
Interference avoidance: DECT 240 channels (10 carrier frequences * 24 timeslots in a frame) Continously checking the signal strength and switch channel if a better is found.
Interference avoidance: BlueTooth 79 carrier frequences (23 in Spain, France, and Japan). A frecuency hopping sequence is pseudorandomly calculated upon the master’s internal clock. Changes channel 1600 times per sec.
Networking In DECT the devices are called ”fixed parts”, FP or ”portable parts”, PP. They have seperate rols in a connection. The fixed part contains a list of portable parts that are allowed to connect. In BlueTooth, all devices are identical ie. all devices can become master och slave in a connection. It is possible to ask an anounymous device for its address over the air.
Provides forwarding of Can messages. The gateway automatically adjusts to the location in a road train. SourceID is changed according to ISO11992. Provides a RS232 serial interface in parallel to the CAN bus. Connections are made and terminated via Can messages. Software written i ANSI C.
Prototype development Connection establishment:
Forwarding CAN messages From CAN : Through Bt-link:
Future Work Hardware Bluetooth Product Qualification Standards