T89C51CC01 Atmel, T89C51CC01 Datasheet - Page 80

• Manufacturer Part Number: T89C51CC01
• Description: Enhanced 8-Bit Microcontroller
• Manufacturer: Atmel

CAN Extended Frame
Figure 40. CAN Extended Frames
Format Co-existence
Bit Timing
Bit Construction
80
Bus Idle
Interframe
Bus Idle
Interframe
Data Frame
Remote Frame
Space
Space
T89C51CC01
SOF
SOF
SOF
SOF
11-bit base identifier
11-bit base identifier
IDT28..18
IDT28..18
SRR IDE
SRR IDE
Arbitration
Arbitration
Field
Field
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.
A message in the CAN extended frame format is likely the same as a message in CAN
standard frame format. The difference is the length of the identifier used. The identifier is
made up of the existing 11-bit identifier (base identifier) and an 18-bit extension (identi-
fier extension). The distinction between CAN standard frame format and CAN extended
frame format is made by using the IDE bit which is transmitted as dominant in case of a
frame in CAN standard frame format, and transmitted as recessive in the other case.
As the two formats have to co-exist on one bus, it is laid down which message has
higher priority on the bus in the case of bus access collision with different formats and
the same identifier / base identifier: The message in CAN standard frame format always
has priority over the message in extended format.
There are three different types of CAN modules available:
To ensure correct sampling up to the last bit, a CAN node needs to re-synchronize
throughout the entire frame. This is done at the beginning of each message with the fall-
ing edge SOF and on each recessive to dominant edge.
One CAN bit time is specified as four non-overlapping time segments. Each segment is
constructed from an integer multiple of the Time Quantum. The Time Quantum or TQ is
the smallest discrete timing resolution used by a CAN node.
18-bit identifier extension
18-bit identifier extension
–
–
–
ID17..0
ID17..0
2.0A - Considers 29 bit ID as an error
2.0B Passive - Ignores 29 bit ID messages
2.0B Active - Handles both 11 and 29 bit ID Messages
RTR
RTR
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
Data
Field
CRC
del.
ACK
Field
ACK
ACK
del.
15-bit CRC
End of
Frame
7 bits
CRC
Field
CRC
Intermission
del.
3 bits
ACK
ACK
Field
Interframe
ACK
Space
del.
(Indefinite)
Bus Idle
End of
Frame
7 bits
4129K–CAN–01/05
Intermission
3 bits
Interframe
Space
(Indefinite)
Bus Idle