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Chapter 19
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19.3 Functions
19.3.1 Determining bus priority
(1)
When a node starts transmission:
• During bus idle, the node that output data first transmits the data.
(2)
When more than one node starts transmission:
• The node that consecutively outputs the dominant level for the longest from
the first bit of the arbitration field has the bus priority (if a dominant level and
a recessive level are simultaneously transmitted, the dominant level is taken
as the bus value).
• The transmitting node compares its output arbitration field and the data level
on the bus.
Table 19-9
Determining bus priority
Level match
Level mismatch
(3)
Priority of data frame and remote frame
• When a data frame and a remote frame are on the bus, the data frame has
priority because its RTR bit, the last bit in the arbitration field, carries a
dominant level.
Caution
If the extended-format data frame and the standard-format remote frame
conflict on the bus (if ID28 to ID18 of both of them are the same), the standard-
format remote frame takes priority.
19.3.2 Bit stuffing
Bit stuffing is used to establish synchronization by appending 1 bit of inverted-
level data if the same level continues for 5 bits, in order to prevent a burst error.
Table 19-10
Bit stuffing
Transmission
Reception
Preliminary User's Manual U17566EE1V2UM00
Continuous transmission
Continuous transmission
During the transmission of a data frame or remote frame,
when the same level continues for 5 bits in the data between
the start of frame and the ACK field, 1 inverted-level bit of
data is inserted before the following bit.
During the reception of a data frame or remote frame, when
the same level continues for 5 bits in the data between the
start of frame and the ACK field, reception is continued after
deleting the next bit.
CAN Controller (CAN)
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