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M16C/5L Group, M16C/56 Group
23.1.16.1 MBNST Bit
The MBNST bit outputs the smallest mailbox number that is searched in each mode of the C0MSMR
register.
In receive mailbox, transmit mailbox, and message lost search modes, the value of the mailbox i.e.,the
search result to be output, is updated as described below:
• When the NEWDATA, SENTDATA, or MSGLOST bit for the output mailbox is set to 0.
• When the NEWDATA, SENTDATA, or MSGLOST bit for a higher-priority mailbox is set to 1.
In receive mailbox search and message lost search modes, the receive FIFO (mailbox [28]) is output
when the receive FIFO is not empty and there are no unread received messages or no lost messages
in any of the normal mailboxes (mailboxes [0] to [23]).
In transmit mailbox search mode, the transmit FIFO (mailbox [24]) is not output.
Table 23.7 lists the behavior of MBNST bit in FIFO mailbox mode.
Table 23.7
Behavior of MBNST Bit in FIFO Mailbox Mode
MBSM Bit
00b
01b
Mailbox [24] is not output.
10b
11b
In channel search mode, the MBNST bit outputs the corresponding channel number. After the C0MSSR
register is read by a program, the next target channel number is output.
23.1.16.2 SEST Bit
The SEST bit is set to 1 when no corresponding mailbox is found after searching all mailboxes.
For example, in transmit mailbox search mode, the SEST bit is set to 1 when no SENTDATA bit for
mailboxes is 1. The SEST bit is set to 0 when at lease one SENTDATA bit is 1.
When the SEST bit is 1, the value of the MBNST bit is undefined.
R01UH0127EJ0110 Rev.1.10
Sep 01, 2011
Mailbox [24]
(Transmit FIFO)
(Receive FIFO)
Mailbox [28] is output when no NEWDATA bit for the normal
mailbox is set to 1 and the receive FIFO is not empty.
Mailbox [28] is not output.
Mailbox [28] is output when no MSGLOST bit for the normal
mailbox is set to 1 and the RFMLF bit is set to 1 in the
receive FIFO.
Mailbox [28] is not output.
23. CAN Module
Mailbox [28]
Page 582 of 803
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