CAN Interface

The CAN-Bus (Controller Area Network-Bus) is a serial communication protocol developed by Bosch to exchange information between electronic control units on automobiles. This system makes possible to share a great amount of information between nodes and control units appended to the system, leading to a major reduction in both the number of sensors required and the quantity of cables in the electrical installation.

The following diagram summarizes the structure of the CAN message 

The CAN frame is mostly autocompleted by the CAN hardware. Nevertheless, there are two frame components that require user interaction: the arbitration field and the data field.

• Arbitration field: In CAN communications, the priority of a message is determined through the content of the arbitration field. The closer that the value of the arbitration field is to zero, the higher the priority of the message, taking precedence over other messages on the CAN bus. CAN bus arbitration is performed at hardware level, ensuring that the highest priority message is transmitted first. As a side effect, the maximum delay of a certain CAN message can be accurately estimated, providing the system with deterministic bound behavior.

  In addition, the remote transmit request (RTR) bit in the arbitration field allows to distinguish between two CAN message types: data frames (containing data for transmission) and remote frames (requesting a transmission from the node determined by the identifier). Setting RTR to 0 generates a data frame, while setting it to 1 generates a remote frame.

• Data field: The content of the data field is application specific.

For further information about the CAN specification, please refer to this link.

CAN and CANopen

The CANopen protocol is based on the CAN specification, and its frame definition is such that one CAN frame is required for each CANopen message.

For further information about CANopen and how the CAN frame is used in CANopen, please refer to the CANopen/CoE section.