Specifications
Overview of the CAN Network
10-3
CAN Controller Module
10.2 Overview of the CAN Network
The controller area network (CAN) uses a serial multimaster communication
protocol that efficiently supports distributed real-time control with a very high
level of data integrity, and communication speeds of up to 1 Mbps. The CAN
bus is ideal for applications operating in noisy and harsh environments, such
as in the automotive and other industrial fields that require reliable commu-
nication.
Prioritized messages of up to eight bytes in data length can be sent on a multi-
master serial bus using an arbitration protocol and an error-detection mecha-
nism for a high level of data integrity.
10.2.1 CAN Protocol Overview
The CAN protocol supports four different frame types for communication:
- Data frames that carry data from a transmitter node to receiver node(s)
- Remote frames that are transmitted by a node to request the transmis-
sion of a data frame with the same identifier
- Error frames that are transmitted by any node on a bus-error detection
- Overload frames that provide an extra delay between the preceding and
the succeeding data frames or remote frames
In addition, CAN specification version 2.0B defines two different formats that
differ in the length of the identifier field: standard frames with an 11-bit identifier
and extended frames with a 29-bit identifier.
CAN standard data frames contain from 44 to 108 bits, and CAN extended
data frames contain 64 to 128 bits. Furthermore, up to 23 stuff bits can be in-
serted in a standard data frame and up to 28 stuff bits in an extended data
frame, depending on the data-stream coding. The overall maximum data
frame length is 131 bits for a standard frame and 156 bits for an extended
frame.
In Figure 10–1, bit fields within the data frame identify:
- Start of the frame
- Arbitration field containing the identifier and the type of message being
sent
- Control field containing the number of data
- Up to 8 bytes of data
- Cyclic redundancy check (CRC)
- Acknowledgment
- End-of-frame bits