h8s-2646 Renesas Electronics Corporation., h8s-2646 Datasheet - Page 603

• Manufacturer Part Number: h8s-2646
• Description: Renesas 16-bit Single-chip Microcomputer H8s Family/h8s/2600 Series
• Manufacturer: Renesas Electronics Corporation.

Mailbox Transmit/Receive Settings: HCAN0, 1 each have 16 mailboxes. Mailbox 0 is receive-
only, while mailboxes 1 to 15 can be set for transmission or reception. Mailboxes that can be set
for transmission or reception must be designated either for transmission use or for reception use
before communication begins. The Initial status of mailboxes 1 to 15 is for transmission (while
mailbox 0 is for reception only). Mailbox transmit/receive settings are not initialized by a software
reset.
• Setting for transmission
• Setting for reception
• Receive-only mailbox (mailbox 0)
Mailbox (Message Control/Data (MCx[x], MDx[x])) Initial Settings: After power is supplied,
all registers and RAM (message control/data, control registers, status registers, etc.) are initialized.
Message control/data (MCx[x], MDx[x]) only are in RAM, and so their values are undefined.
Initial values must therefore be set in all the mailboxes (by writing 0s or 1s).
Setting the Message Transmission Method: Either of the following message transmission
methods can be selected with the message transmission method bit (MCR2) in the master control
register (MCR):
a. Transmission order determined by message identifier priority
b. Transmission order determined by mailbox number priority
When a is selected, if a number of messages are designated as waiting for transmission (TXPR =
1), the message with the highest priority set in the message identifier (MCx[5] to MCx[8]) is
stored in the transmit buffer. CAN bus arbitration is then carried out for the message in the
transmit buffer, and message transmission is performed when the transmission right is acquired.
When the TXPR bit is set, internal arbitration is performed again, and the highest-priority message
is found and stored in the transmit buffer.
Transmit mailbox setting (mailboxes 1 to 15)
Clearing a bit to 0 in the mailbox configuration register (MBCR) designates the corresponding
mailbox for transmission use. After a reset, mailboxes are initialized for transmission use, so
this setting is not necessary.
Transmit/receive mailbox setting (mailboxes 1 to 15)
Setting a bit to 1 in the mailbox configuration register (MBCR) designates the corresponding
mailbox for reception use. When setting mailboxes for reception, to improve message
transmission efficiency, high-priority messages should be set in low-to-high mailbox order
(priority order: mailbox 1 > mailbox 15).
No setting is necessary, as this mailbox is always used for reception.
Section 15 Controller Area Network (HCAN)
Rev. 5.00 Sep 22, 2005 page 577 of 1136
REJ09B0257-0500