CHAPTER 19 FCAN CONTROLLER (V850/SC3)
User’s Manual U15109EJ3V0UD
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19.11 Functions
19.11.1 Determination of bus priority
(1) When one node has starting transmitting
•
In bus idle mode, the node that outputs data first starts transmitting.
(2) When several nodes have started transmitting
•
The node that outputs the longest string of consecutive dominant-level bits starting from the first bit in the
arbitration field has top priority for bus access (dominant-level bits take precedence due to wired-OR bus
arbitration).
•
The transmitting node compares the arbitration field which it has output and the bus data level.
Table 19-24. Determination of Bus Priority
Matched levels
Transmission continues
Mismatched levels
When a mismatch is detected, data output stops at the next bit, and the
operation switches to reception.
(3) Priority between data frame and remote frame
•
If a bus conflict occurs between a data frame and a remote frame, the data frame takes priority because its
last bit (RTR) is dominant level.
19.11.2 Bit stuffing
Bit stuffing is when one bit of inverted data is added for resynchronization to prevent burst errors when the same
level is maintained for five consecutive bits.
Table 19-25. Bit Stuffing
Transmit
When transmitting data frames and remote frames, if the same level is maintained for at least
five bits between the start of frame and CRC fields, one bit of data whose level is inverted from
the previous level is inserted before the next bit.
Receive
When receiving data frames and remote frames, if the same level is maintained for at least five
bits between the start of frame and CRC fields, the next bit of data is deleted before reception is
resumed.
19.11.3 Multimasters
Since bus priority is determined based on the identifier, any node can be used as the bus master.
19.11.4 Multi-cast
Even when there is only one transmitting node, the same identifier can be set for several nodes, so that the same
data can be received by several nodes at the same time (this is called “multi-casting”).