CAN Overview

The data frame is the fundamental unit of data transfer on a CAN network. The following figure shows a simplified view of the CAN data frame.

CAN Data Frame

When multiple CAN devices transmit a frame at the same time, the identifier (ID) resolves the collision. The highest priority ID continues, and the lower priority IDs retry immediately afterward. The ISO 11898 CAN standard specifies two ID formats: the standard format of 11 bits and the extended format of 29 bits.

The ID is followed by a length code that specifies the number of data bytes in the frame. The length ranges from 0 to 8 data bytes. The ID value determines the meaning of the data bytes.

In addition to the data frame, the CAN standard specifies the remote frame. The remote frame includes the ID, but no data bytes. A CAN device transmits the remote frame to request that another device transmit the associated data frame for the ID. In other words, the remote frame provides a mechanism to poll for data.

The preceding information provides a simplified description of CAN frames. The CAN frame format includes many other fields, such as for error checking and acknowledgement. For more detailed information on the ISO 11898 CAN standard, refer to Summary of the CAN Standard.