Introduction to
Controller Area Network - CAN
Introduction to
Controller Area Network - CAN
CAN
was developed initially for use in the automotive industry. As cars contained
increasing amounts of electronic modules, these needed to communicate with each
other. This lead to a complex interconnection of various modules.
Figure 1.
Figure 1 above shows just a few of the electronic systems in a modern car. The extra interconnect required cables several miles in length in total. Adding extra systems meant link those up to possibly several existing systems.
CAN was invented to over come this problem of point-to-point connection by introducing a serial bus that connected to each system (node). Each node on the CAN system has a CAN interface that it uses to transmit and receive information.
Figure 2.
The use of CAN greatly simplified the routing of cables as shown in figure 2. Adding extra nodes to the system is now a simple task of connecting the new node to the CAN bus, having done so it can now communicate with all other nodes on the bus.
CAN is internationally standardized by the International Standardization Organization (ISO) and the Society of Automotive Engineers (SAE).
There are two possible states for the CAN bus. Dominate (zero) or recessive (one). The bus will only be recessive if all the nodes on the bus transmit a recessive bit. If a single node transmits a dominate bit the CAN bus will be dominate (zero). Each node has a receive (R) and transmit (T) line.
Figure 3.
Using the layout shown in figure the dominate/recessive CAN bus states are implemented. If both nodes transmit a recessive bit, both of the transistors are disabled and the bus becomes recessive (one). If either one of the nodes transmit a dominate (zero), the transistor becomes enabled and the CAN bus voltage will be connected to ground leaving the CAN bus in a dominate (zero) state.