RL78/D1A User's Manual: Hardware - Renesas

Under development
Preliminary document
Specifications in this document are tentative and subject to change.
RL78/D1A CHAPTER 14 CAN CONTROLLER
14.3 Functions
14.3.1 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 outputs the dominant level for the longest consecutively from the first bit of the arbitration field
acquires 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.
Level match Continuous transmission
Table 14-9. Determining Bus Priority
Level mismatch Stops transmission at the bit where mismatch is detected and starts reception at the following bit
(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 frames takes priority.
14.3.2 Bit stuffing
Bit stuffing is used to establish synchronization by appending 1-bit inverted data if the same level continues for 5 bits, in
order to prevent a burst error.
Table 14-10. Bit Stuffing
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.
Reception 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.
14.3.3 Multi masters
As the bus priority (a node acquiring transmit functions) is determined by the identifier, any node can be the bus master.
14.3.4 Multi cast
Although there is one transmitting node, two or more nodes can receive the same data at the same time because the
same identifier can be set to two or more nodes.
14.3.5 CAN sleep mode/CAN stop mode function
The CAN sleep mode/CAN stop mode function puts the CAN controller in waiting mode to achieve low power
consumption.
The controller is woken up from the CAN sleep mode by bus operation but it is not woken up from the CAN stop mode
by bus operation (the CAN stop mode is controlled by CPU access).
R01UH0317EJ0004 Rev. 0.04 797
Feb. 22, 2013