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Section 20 Controller Area Network
Page 1068 of 2108 R01UH0134EJ0400 Rev. 4.00
Sep 24, 2014
SH7262 Group, SH7264 Group
If, at any time, a reference message cannot be detected on the CAN Bus, and the cycle time
CYCTR reaches TCMR2, this module automatically aborts all pending transmissions (including
the Reference Message).
The following is the sequence to request further transmission in Time Triggered mode.
End Of Frame
CAN Bus
No
No
Idle (wait for Time-Trigger)
Compare match
Bus Idle?
Transmission Start
No Arbitration on Bus
Update data before next match
of Tx-Trigger Time
Mailbox[x] is ready
to be updated for
next transmission
Clear TXACK[x]
TXACK[x] = 1 ?
IRR8 = 1 ?
Ye s
Ye s
No
Waiting for
Interrupt
Waiting for
Interrupt
Figure 20.21 Message transmission request
S/W has to ensure that a message is updated before a Tx trigger for transmission occurs.
When the CYCTR reaches to TTT (Tx-Trigger Time) of a Mailbox and CCR matches with the
programmed cycle for transmission, this module immediately transfers the message into the Tx
buffer. At this point, this module will attempt a transmission within the specified Time Enable
Window. If this module misses this time slot, it will suspend the transmission request up to the
next Tx Trigger, keeping the corresponding TXPR bit set to '1' if the transmission is periodic
(Mailbox-24 to 30). There are three factors that may cause this module to miss the time slot –
1. The CAN bus currently used
2. An error on the CAN bus during the time triggered message transmission
3. Arbitration loss during the time triggered message transmission