
271
μPD780948, μPD78F0948, μPD780949, μPD78F0949
18.2
Function
18.2.1 Bus priority decision
(1) When 1 node starts transmission
During bus idle, the node having the output data can transmit.
(2) When more than 2 nodes start transmission
The node with the lower identifier wins the arbitration.
The transmission node compares its output arbitration field and the data level on the bus.
It looses arbitration, when it outputs recessive level and sees dominant on bus.
Table 18-10: Bus Priority Decision
(3) Priority of data frame and remote frame
When the data frame and remote frame are on the bus, the data frame has priority in which RTR is
'Dominant level'. The data frame wins the arbitration.
18.2.2 Bit stuffing
When the same level continues for more than 5 bits, bit stuffing (insert 1 bit with inverse level) takes place
to prevent an error.
Table 18-11: Bit Stuffing
Conformity of Level
Continuous Transmission
Non-conformity of level
The data output is stopped from the next bit and reception operation starts.
18.2.3 Multi master
As the bus priority is determined by the identifier, any node can be the bus master.
18.2.4 Multi cast
If there are different nodes, is only one, an identifier has to be transmitted only one node. The same
reception can be done in more than 2 nodes simultaneously.
18.2.5
Sleep mode/Stop function
This is a function to put the CAN controller in waiting mode to achieve low power consumption. The SLEEP
mode is defined like in the CAN specification.
Additional to this SLEEP mode, which can be woken up by bus activities, the STOP mode is fully controlled
by the CPU device.
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 ACK field, 1 bit level with reverse level of data
is inserted before the following bit.
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 ACK field, the reception is continued by deleting
following 1 bit.
Reception