NXP Semiconductors MWCT101 S Series, Reference Manual

Page: 1660 / 1761

49.5.2.1 Lowest-number mailbox first
If CTRL1[LBUF] is asserted, the first (lowest number) active Tx mailbox found is the
arbitration winner. MCR[LPRIOEN] has no effect when CTRL1[LBUF] is asserted.
49.5.2.2 Highest-priority mailbox first
If CTRL1[LBUF] 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 the MCR[LPRIOEN] setting.
49.5.2.2.1 Local priority disabled
If MCR[LPRIOEN] 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 49-21. 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)
49.5.2.2.2 Local priority enabled
To enable local priority, MCR[LPRIOEN] must be asserted. In this case the mailbox
PRIO field is included at the very left of the arbitration value (see the following table).
Functional description
MWCT101xS Series Reference Manual, Rev. 3, 07/2019
1660 NXP Semiconductors