h8s-2628 Renesas Electronics Corporation., h8s-2628 Datasheet - Page 445

• Manufacturer Part Number: h8s-2628
• Description: Renesas 16-bit Single-chip Microcomputer H8s Family/h8s/2600 Series
• Manufacturer: Renesas Electronics Corporation.

Mailbox Transmit/Receive Settings: The HCAN has 16 mailboxes. Mailbox 0 is receive-only,
while mailboxes 15 to 1 can be set for transmission or reception. The initial status of mailboxes 15
to 1 is for transmission. Mailbox transmit/receive settings are not initialized by a software reset.
Clearing a bit to 0 in the mailbox configuration register (MBCR) designates the corresponding
mailbox for transmission use, whereas a setting of 1 in MBCR designates the corresponding
mailbox for reception use. When setting mailboxes for reception, in order to improve message
reception efficiency, high-priority messages should be set in low-to-high mailbox order.
Mailbox (Message Control/Data) Initial Settings: Message control/data are held in RAM, and
so their initial values are undefined after power is supplied. Initial values must therefore be set in
all the mailboxes (by writing 0s or 1s).
Setting the Message Transmission Method: The following two kinds of message transmission
methods are available.
Either of the message transmission methods can be selected with the message transmission method
bit (MCR2) in the master control register (MCR): When messages are set to be transmitted
according to the message identifier priority, if several messages are designated as waiting for
transmission (TXPR = 1), the message with the highest priority in the message identifier is stored
in the transmit buffer. CAN bus arbitration is then carried out for the message stored in the
transmit buffer, and the message is transmitted when the transmission right is acquired. When the
TXPR bit is set, the highest-priority message is found and stored in the transmit buffer.
When messages are set to be transmitted according to the mailbox number priority, if several
messages are designated as waiting for transmission (TXPR = 1), messages are stored in the
transmit buffer in low-to-high mailbox order. CAN bus arbitration is then carried out for the
message stored in the transmit buffer, and the message is transmitted when the transmission right
is acquired.
15.4.3
Messages are transmitted using mailboxes 15 to 1. The transmission procedure after initial settings
is described below, and a transmission flowchart is shown in figure 15.9.
Transmission order determined by message identifier priority
Transmission order determined by mailbox number priority
Message Transmission
Section 15 Controller Area Network (HCAN)
Rev. 3.00 Oct 04, 2005 page 405 of 598
REJ09B0155-0300