SAM7X256_14 Datasheet, PDF (484/662 Pages) ATMEL Corporation – ARM-based Flash MCU

36.6 CAN Controller Features
36.6.1 CAN Protocol Overview
The Controller Area Network (CAN) is a multi-master serial communication protocol that efficiently 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:
 Data frames: They carry data from a transmitter node to the receiver nodes. The overall maximum data frame
length is 108 bits for a standard frame and 128 bits for an extended frame.
 Remote frames: A destination node can request data from the source by sending a remote 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.
 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 data frames or remote
frames.
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 automatically handled by the CAN controller under supervision of the software
application.
36.6.2 Mailbox Organization
The CAN module has 8 buffers, also called channels or mailboxes. An identifier that corresponds 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.
36.6.2.1 Message Acceptance Procedure
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.
SAM7X Series [DATASHEET]
6120K–ATARM–11-Feb-14
484