h8s-2635 Renesas Electronics Corporation., h8s-2635 Datasheet - Page 728

• Manufacturer Part Number: h8s-2635
• Description: Renesas 16-bit Single-chip Microcomputer H8s Family/h8s/2600 Series
• Manufacturer: Renesas Electronics Corporation.

Section 16 Controller Area Network (HCAN)
(7) Register retention during standby
All HCAN registers are initialized in hardware standby mode and software standby mode.
(8) Usage of bit manipulation instructions
The HCAN status flags are cleared by writing 1, so do not use a bit manipulation instruction to
clear a flag.
When clearing a flag, use the MOV instruction to write 1 to only the bit that is to be cleared.
(9) Operation of TXCR in HCAN
1. When the transmit wait cancel register (TXCR) is used to cancel messages awaiting
2. If TXPR is set, resulting in transmission wait status, when a transition to bus off status takes
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transmission from a mailbox waiting to transmit, the bits corresponding to TXCR and the
transmit wait register (TXPR) are sometimes not cleared in spite of the fact that transmission
was cancelled. This situation can arise when all of the following conditions are met.
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place, cancellation cannot be performed even if TXCR is set during bus off status because the
internal state machine does not operate. After recovery from bus off status, the message is
cancelled after one message is either sent or generates a transmission error. The following
countermeasure should be taken with regard to clearing messages following recovery from bus
off status.
The HRxD pin is stuck at 1 because of a CAN bus error, etc.
One or more mailboxes are waiting to transmit (or transmitting).
Transmission of a message in a mailbox that is transmitting is cancelled using TXCR.
When this situation occurs the message is not cancelled. However, since TXPR and TXCR
continue to incorrectly display the status of the message as in the process of being
cancelled, it is not possible to restart transmission even when the HRxD pin is no longer
stuck at 1 and the CAN bus is restored to normal status. If there are two or more messages
to be transmitted, those messages that are not in the process of being sent are cancelled and
the messages in the process of being sent remain in that status.
To avoid the situation described above, either of the following two countermeasures should
be implemented.
Do not use TXCR to cancel transmission of messages. This will ensure that TXPR is
cleared and HCAN operates normally after transmission completes normally following
recovery by the CAN bus.
If it is necessary to cancel transmission of a message, write continuously to bit 1
corresponding to TXCR until the bits corresponding to TXCR become 0. This will ensure
that TXPR and TXCR are cleared and that HCAN is restored to normal operation.