at91sam9263 ATMEL Corporation, at91sam9263 Datasheet - Page 660

• Manufacturer Part Number: at91sam9263
• Description: At91 Arm Thumb Microcontrollers
• Manufacturer: ATMEL Corporation

37.6
37.6.1
37.6.2
37.6.2.1
660
CAN Controller Features
AT91SAM9263 Preliminary
CAN Protocol Overview
Mailbox Organization
Message Acceptance Procedure
The Controller Area Network (CAN) is a multi-master serial communication protocol that effi-
ciently supports real-time control with a very high level of security with bit rates up to 1 Mbit/s.
The CAN protocol supports four different frame types:
The Atmel CAN controller provides the CPU with full functionality of the CAN protocol V2.0 Part
A and V2.0 Part B. It minimizes the CPU load in communication overhead. The Data Link Layer
and part of the physical layer are automatically handled by the CAN controller itself.
The CPU reads or writes data or messages via the CAN controller mailboxes. An identifier is
assigned to each mailbox. The CAN controller encapsulates or decodes data messages to build
or to decode bus data frames. Remote frames, error frames and overload frames are automati-
cally handled by the CAN controller under supervision of the software application.
The CAN module has 16 buffers, also called channels or mailboxes. An identifier that corre-
sponds to the CAN identifier is defined for each active mailbox. Message identifiers can match
the standard frame identifier or the extended frame identifier. This identifier is defined for the first
time during the CAN initialization, but can be dynamically reconfigured later so that the mailbox
can handle a new message family. Several mailboxes can be configured with the same ID.
Each mailbox can be configured in receive or in transmit mode independently. The mailbox
object type is defined in the MOT field of the CAN_MMRx register.
If the MIDE field in the CAN_MIDx register is set, the mailbox can handle the extended format
identifier; otherwise, the mailbox handles the standard format identifier. Once a new message is
received, its ID is masked with the CAN_MAMx value and compared with the CAN_MIDx value.
If accepted, the message ID is copied to the CAN_MIDx register.
• Data frames: They carry data from a transmitter node to the receiver nodes. The overall
• Remote frames: A destination node can request data from the source by sending a remote
• Error frames: An error frame is generated by any node that detects a bus error.
• Overload frames: They provide an extra delay between the preceding and the successive
maximum data frame length is 108 bits for a standard frame and 128 bits for an extended
frame.
frame with an identifier that matches the identifier of the required data frame. The appropriate
data source node then sends a data frame as a response to this node request.
data frames or remote frames.
6249D–ATARM–20-Dec-07