Transmit Control Register - Toshiba TXZ+ Series Reference Manual

TXZ+ Family
CAN Controller

Transmit Control Register

Transmission control consists of two registers. One is the transmission request set register [CANxTRS], and the
other is the transmission request reset register [CANxTRR]. Therefore it is possible to clear the transmission
request without generating a conflict in the handling of the transmission mailboxes in the state-machine.
This mechanism also prevents clearing the transmission request of a mailbox to which transmission is already in
progress.
When a write of data and the ID to mailbox n configured as a transmission mailbox ([CANxMD]<MDn>=0) is
performed and access to mailbox n is enabled ([CANxMC]<MCn>=1), setting the [CANxTRS]<TRSn> bit to "1"
causes the messages in mailbox n to be transmitted.
If there is more than one mailbox configured as a transmission mailbox and more than one corresponding TRS bit
is set, then the messages will be sent in the selected order. The order of transmission depends on the <MTOS> bit
in the master control register [CANxMCR].
If the [CANxMCR]<MTOS> bit is "0", the mailbox with the lower number has the higher priority. For example, if
the mailboxes CANxMB0, CANxMB2, and CANxMB5 are configured as transmission mailboxes and the
corresponding [CANxTRS]<TRSn> bits are set to "1", then the messages will be transmitted in the following
order: CANxMB0, CANxMB2, and CANxMB5. If a new transmission request is set for CANxMB0 during
processing of the CANxMB2 message, then in the next internal arbitration-run, CANxMB0 is selected for the next
transmission message and transmission of the CANxMB0 message starts after CANxMB2 transmission is
completed.
This also happens if an arbitration lost error occurs while the CANxMB2 message is being transmitted.
The CANxMB0 message will be sent instead of the CANxMB2 lost in arbitration.
If the [CANxMCR]<MTOS> bit is "1", the mailbox with the highest priority ID among those mailboxes for which
transmission is requested will be transmitted. In a transmission after an arbitration lost error occurred also, the
message in the mailbox with the highest priority ID among those mailboxes for which transmission is requested at
the time will be transmitted.
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Rev. 1.0