AT89C51CC03U-S3SIM ATMEL [ATMEL Corporation], AT89C51CC03U-S3SIM Datasheet - Page 86

• Manufacturer Part Number: AT89C51CC03U-S3SIM
• Description: Enhanced 8-bit MCU with CAN Controller and Flash Memory
• Manufacturer: ATMEL [ATMEL Corporation]

CAN Controller
CAN Protocol
Principles
Message Formats
Can Standard Frame
Figure 43. CAN Standard Frames
86
AT89C51CC03
Interframe
Interframe
Data Frame
Remote Frame
Bus Idle
Space
Bus Idle
Space
SOF
SOF
SOF
SOF
11-bit identifier
11-bit identifier
ID10..0
ID10..0
Arbitration
Arbitration
Field
Field
The CAN Controller provides all the features required to implement the serial communi-
cation protocol CAN as defined by BOSCH GmbH. The CAN specification as referred to
by ISO/11898 (2.0A and 2.0B) for high speed and ISO/11519-2 for low speed. The CAN
Controller is able to handle all types of frames (Data, Remote, Error and Overload) and
achieves a bitrate of 1-Mbit/sec at 8 MHz
Note:
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.
The CAN protocol supports two message frame formats, the only essential difference
being in the length of the identifier. The CAN standard frame, also known as CAN 2.0 A,
supports a length of 11 bits for the identifier, and the CAN extended frame, also known
as CAN 2.0 B, supports a length of 29 bits for the identifier.
A message in the CAN standard frame format begins with the "Start Of Frame (SOF)",
this is followed by the "Arbitration field" which consist of the identifier and the "Remote
Transmission Request (RTR)" bit used to distinguish between the data frame and the
data request frame called remote frame. The following "Control field" contains the "IDen-
tifier Extension (IDE)" bit and the "Data Length Code (DLC)" used to indicate the
RTR IDE
RTR IDE
1. At BRP = 1 sampling point will be fixed.
r0
r0
Control
Control
Field
Field
4-bit DLC
4-bit DLC
DLC4..0
DLC4..0
15-bit CRC
CRC
Field
0 - 8 bytes
Data
Field
CRC
del.
ACK
Field
ACK
ACK
del.
1
Crystal frequency in X2 mode.
End of
Frame
7 bits
15-bit CRC
CRC
Field
Intermission
3 bits
CRC
del.
Interframe
ACK
Space
Field
ACK
(Indefinite)
ACK
Bus Idle
del.
End of
Frame
7 bits
4182I–CAN–06/05
Intermission
3 bits
Interframe
Space
(Indefinite)
Bus Idle