
250
Chapter 16
CAN Controller
User’s Manual U16504EE1V1UD00
16.2 Function
16.2.1 Arbitration
If two or more nodes happen to start transmission in coincidence, the access conflict is solved by a bit-
wise arbitration mechanism during transmission of the ARBITRATION FIELD.
(1) When a node starts transmission:
During bus idle, the node having the output data can transmit.
(2) When more than one node starts transmission:
The node with the lower identifier wins the arbitration.
Any transmitting node compares its output arbitration field and the data level on the bus.
It looses arbitration, when it sends recessive level and reads dominant from bus.
Table 16-9:
Arbitration
(3) Priority of data frame and remote frame:
When a data frame and remote frame with the same message identifier are on the bus, the data
frame has priority because its RTR bit carries 'Dominant level'. The data frame wins the
arbitration.
16.2.2 Bit Stuffing
When the same level continues for more than 5 bits, bit stuffing (insert 1 bit with inverse level) takes
place.
Due to this a resynchronization of the bit timing can be done at least every 10 bits.
Nodes detecting an error condition send an error frame, violating the bit stuff rule and indicating
this message to be erroneous for all nodes.
Table 16-10:
Bit Stuffing
Level Detection
Status of Arbitrating Node
Conformity of Level
Continuous Transmission
Non-conformity of
Level
The data output is stopped from the next bit and reception operation starts.
Transmission
During the transmission of a data frame and a remote frame, when the same level continues
for 5 bits in the data between the start of frame and the ACK field, 1 bit level with reverse level
of data is inserted before the following bit.
Reception
During the reception of a data frame and a remote frame, when the same level continues for
5 bits in the data between the start of frame and the ACK field, the reception is continued by
deleting the next bit.