HD64F2638F20J Datasheet, PDF (728/1512 Pages) Renesas Technology Corp – Renesas 16-Bit Single-Chip Microcomputer H8S Family/H8S/2600 Series

Section 16 Controller Area Network (HCAN)
H8S/2639, H8S/2638, H8S/2636,
H8S/2630, H8S/2635 Group
(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) HCAN TXCR Operation
1. When the transmit wait cancel register (TXCR) is used to cancel transmission of the
message in a mailbox waiting for transmission, the corresponding bit in TXCR and the
transmit wait register (TXPR) may not be cleared even after the transmission is canceled.
This occurs when the following conditions are all satisfied.
[Conditions]
⎯ The HRxD pin is tied to "1" because of a CAN bus error, etc.
⎯ There is one or more mailboxes waiting for transmission or transmitting.
⎯ Ongoing message transmission from a mailbox is canceled by TXCR.
If this occurs, the transmission is canceled but TXPR and TXCR continue to indicate a
wrong status telling that a message is being cancelled. As a result, transmission cannot be
restarted even after the HRxD pin is released from the tied state and the CAN bus has
recovered. If there are two or more messages for transmission, a message which is not
being transmitted is canceled and a message being transmitted retains its state.
To avoid this, take either of the following countermeasures.
[Countermeasures]
⎯ Do not cancel transmission by TXCR. Transmission will be completed after the CAN
bus has recovered, then TXPR is cleared and the HCAN operates normally.
⎯ To cancel transmission, write 1 to the corresponding bit in TXCR repeatedly until the
bit becomes 0. TXPR and TXCR are cleared, and the HCAN operates normally.
2. When the bus-off state is entered while any mailbox is waiting for transmission with TXPR
set, transmission cannot be canceled even if TXCR is set because the internal state machine
does not operate during the bus-off state. Because of this, on recovery from the bus-off
state, one message will be transmitted or the message will be canceled with a transmission
error. For message clearing on recovery from the bus-off state, take the following
countermeasure.
Page 678 of 1458
REJ09B0103-0800 Rev. 8.00
May 28, 2010