NXP Semiconductors KE1xF Series, Reference Manual, Page: 1436 / 1483

The arbitration process selects the winner among the active Tx Mailboxes at the end of
the scan according to both CAN_CTRL1[LBUF] and CAN_MCR[LPRIOEN] bits
settings.
50.5.2.1 Lowest-number Mailbox first
If CAN_CTRL1[LBUF] bit is asserted the first (lowest number) active Tx Mailbox found
is the arbitration winner. CAN_MCR[LPRIOEN] bit has no effect when
CAN_CTRL1[LBUF] is asserted.
50.5.2.2 Highest-priority Mailbox first
If CAN_CTRL1[LBUF] bit is negated, then the arbitration process searches the active Tx
Mailbox with the highest priority, which means that this Mailbox’s frame would have a
higher probability to win the arbitration on CAN bus when multiple external nodes
compete for the bus at the same time.
The sequence of bits considered for this arbitration is called the arbitration value of the
Mailbox. The highest-priority Tx Mailbox is the one that has the lowest arbitration value
among all Tx Mailboxes.
If two or more Mailboxes have equivalent arbitration values, the Mailbox with the lowest
number is the arbitration winner.
The composition of the arbitration value depends on CAN_MCR[LPRIOEN] bit setting.
50.5.2.2.1 Local Priority disabled
If CAN_MCR[LPRIOEN] bit is negated the arbitration value is built in the exact
sequence of bits as they would be transmitted in a CAN frame (see the following table) in
such a way that the Local Priority is disabled.
Table 50-10. Composition of the arbitration value when Local Priority is disabled
Format Mailbox Arbitration Value (32 bits)
Standard (IDE = 0) Standard ID (11
bits)
RTR (1 bit) IDE (1 bit) - (18 bits) - (1 bit)
Extended (IDE = 1) Extended ID[28:18]
(11 bits)
SRR (1 bit) IDE (1 bit) Extended ID[17:0]
(18 bits)
RTR (1 bit)
Functional description
Kinetis KE1xF Sub-Family Reference Manual, Rev. 4, 06/2019
1436 NXP Semiconductors