AT90CAN128-16AE ATMEL Corporation, AT90CAN128-16AE Datasheet - Page 230

• Manufacturer Part Number: AT90CAN128-16AE
• Description: 8-bit Avr Microcontroller With 128K Bytes of Isp Flash And CAN Controller.flash (Kbytes) 128 Vcc (V) 2.7-5.5 EEPROM (Kbytes) 4 SRAM (bytes) 4K CAN (mess. Obj.) 15
• Manufacturer: ATMEL Corporation

Message Formats
Can Standard Frame
Figure 108. CAN Standard Frames
CAN Extended Frame
Figure 109. CAN Extended Frames
230
Interframe
Interframe
Bus Idle
Bus Idle
Data Frame
Remote Frame
Space
Space
AT90CAN128
SOF
SOF
SOF
SOF
11-bit base identifier
11-bit base identifier
IDT28..18
IDT28..18
Interframe
Interframe
Data Frame
Remote Frame
Bus Idle
Space
Bus Idle
Space
SRR IDE
SRR IDE
SOF
SOF
SOF
SOF
Arbitration
Arbitration
Field
Field
11-bit identifier
11-bit identifier
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
number of following data bytes in the "Data field". In a remote frame, the DLC contains
the number of requested data bytes. The "Data field" that follows can hold up to 8 data
bytes. The frame integrity is guaranteed by the following "Cyclic Redundant Check
(CRC)" sum. The "ACKnowledge (ACK) field" compromises the ACK slot and the ACK
delimiter. The bit in the ACK slot is sent as a recessive bit and is overwritten as a domi-
nant bit by the receivers which have at this time received the data correctly. Correct
messages are acknowledged by the receivers regardless of the result of the acceptance
test. The end of the message is indicated by "End Of Frame (EOF)". The "Intermission
Frame Space (IFS)" is the minimum number of bits separating consecutive messages. If
there is no following bus access by any node, the bus remains idle.
ID10..0
ID10..0
18-bit identifier extension
18-bit identifier extension
Arbitration
Arbitration
Field
Field
ID17..0
ID17..0
RTR IDE r0
RTR IDE r0
RTR
RTR
Control
Control
Field
Field
4-bit DLC
4-bit DLC
DLC4..0
DLC4..0
r1
r1
Control
Control
Field
Field
r0
r0
4-bit DLC
4-bit DLC
DLC4..0
DLC4..0
15-bit CRC
CRC
Field
0 - 8 bytes
15-bit CRC
Field
CRC
Data
del.
CRC
Field
ACK
0 - 8 bytes
Field
ACK
Field
Data
ACK
CRC
del.
del.
ACK
ACK
Field
End of
Frame
7 bits
ACK
del.
15-bit CRC
15-bit CRC
CRC
Field
End of
Frame
7 bits
Intermission
CRC
Field
3 bits
CRC
del.
Interframe
CRC
Intermission
ACK
Space
del.
Field
ACK
3 bits
(Indefinite)
ACK
ACK
Bus Idle
del.
ACK
Field
Interframe
ACK
Space
del.
(Indefinite)
End of
Frame
7 bits
Bus Idle
End of
Frame
7 bits
Intermission
3 bits
4250C–CAN–03/04
Intermission
3 bits
Interframe
Interframe
Space
Space
(Indefinite)
Bus Idle
(Indefinite)
Bus Idle