NEC V850E/PH2, User Manual

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Chapter 18 AFCAN Controller
User’s Manual U16580EE3V1UD00
18.3 Functions
18.3.1 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 arbitra-
tion field has the bus priority (if a dominant level and a recessive level are simultaneously transmit-
ted, the dominant level is taken as the bus value).
• The transmitting node compares its output arbitration field and the data level on the bus.
(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.
Remark: 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 pri-
ority.
18.3.2 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 18-9: Determining bus priority
Level match Continuous transmission
Level mismatch Stops transmission at the bit where mismatch is detected
and starts reception at the following bit
Table 18-10: 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.