CAN or Controller Area Network is a asynchronous serial protocol designed by Bosch in 1983. It is extremely common in many markets including Automotive, Medical and Industrial because it has been industry proven to be robust, reliable and safer than many other alternatives.
CAN is a Multi-Drop, shared bus that solves many challenges associated with this topology in its controller. CAN notes are able to broadcast information on the bus and many higher level protocols such as CAN Open further extent the functionality of CAN to include client server relationships, multicast and node state management.
CAN uses Carrier Sense, Multiple Access to Arbitrate the bus and determine which node address has permission to communicate. This inherently allows the bus to prioritize access with the lowest node id getting priority and therefore helps determinism for high priority nodes. This is one of the most critical bus attributes in automotive where a engine control system would require higher priority and determinism than a power window control switch.
The CAN packet structure includes a node ID, Data Payload as well as a Cyclic Redundancy Check that verifies the validity of the packet. Through use of a ACK and NAK slot, nodes can also signal the transmitter if the packet was corrupted and a re-transmission will occur automatically.
With all of these unique features of CAN implemented at the controller level, it dramatically simplifies the software stack needed in the equivalent RS-485 serial network, this is one of many reasons why CAN is so popular.
CAN’s standard physical layer is differential in nature with dominate and recessive states, it also requires termination making it very noise immune, particularly for common mode effects. The Physical layer is also capable of detecting short and open circuits for further diagnostics.
In some conditions, CAN can operate at up to 1 Mbaud however clock accuracy and cable capacitance can be factors that would prevent this speed from functioning reliably.
For many years, patent royalties were required to be paid to Bosch for their invention of CAN. Today virtually all of these patents are expired and CAN may be integrated into an ASIC without royalty.
Triad has experience with CAN both with the digital controller the physical layer transceiver. Our Mixed Signal Integration Architects are very familiar with the operation of CAN networks and consideration associated with employing them in an ASIC.