MEGA128CAN Datasheet, PDF (229/413 Pages) ATMEL Corporation – Microcontroller WITH 128K BYTES OF ISP FLASH AND CAN CONTROLLER

AT90CAN128
Controller Area Network - CAN
The Controller Area Network (CAN) protocol is a real-time, serial, broadcast protocol
with a very high level of security. The AT90CAN128 CAN controller is fully compatible
with the CAN Specification 2.0 Part A and Part B. It delivers the features required to
implement the kernel of the CAN bus protocol according to the ISO/OSI Reference
Model:
• The Data Link Layer
- the Logical Link Control (LLC) sublayer
- the Medium Access Control (MAC) sublayer
• The Physical Layer
- the Physical Signalling (PLS) sublayer
- not supported - the Physical Medium Attach (PMA)
- not supported - the Medium Dependent Interface (MDI)
The CAN controller is able to handle all types of frames (Data, Remote, Error and Over-
load) and achieves a bitrate of 1 Mbit/s.
Features
• Full Can Controller
• Fully Compliant with CAN Standard rev 2.0 A and rev 2.0 B
• 15 MOb (Message Object) with their own:
– 11 bits of Identifier Tag (rev 2.0 A), 29 bits of Identifier Tag (rev 2.0 B)
– 11 bits of Identifier Mask (rev 2.0 A), 29 bits of Identifier Mask (rev 2.0 B)
– 8 Bytes Data Buffer (Static Allocation)
– Tx, Rx, Frame Buffer or Automatic Reply Configuration
– Time Stamping
• 1 Mbit/s Maximum Transfer Rate at 8 MHz
• TTC Timer
• Listening Mode (for Spying or Autobaud)
CAN Protocol
Principles
The CAN protocol is an international standard defined in the ISO 11898 for high speed
and ISO 11519-2 for low speed.
CAN is based on a broadcast communication mechanism. This broadcast communica-
tion is achieved by using a message oriented transmission protocol. These messages
are identified by using a message identifier. Such a message identifier has to be unique
within the whole network and it defines not only the content but also the priority of the
message.
The priority at which a message is transmitted compared to another less urgent mes-
sage is specified by the identifier of each message. The priorities are laid down during
system design in the form of corresponding binary values and cannot be changed
dynamically. The identifier with the lowest binary number has the highest priority.
Bus access conflicts are resolved by bit-wise arbitration on the identifiers involved by
each node observing the bus level bit for bit. This happens in accordance with the "wired
and" mechanism, by which the dominant state overwrites the recessive state. The com-
petition for bus allocation is lost by all nodes with recessive transmission and dominant
observation. All the "losers" automatically become receivers of the message with the
highest priority and do not re-attempt transmission until the bus is available again.
4250E–CAN–12/04
229