Renesas H8S Series Hardware Manual page 462

Section 15 Controller Area Network (HCAN)
remaining mailboxes. It is therefore possible for a message matching mailbox 0 to be received
by another mailbox. Note that the same message cannot be stored in more than one of
mailboxes 1 to 15. On receiving a message, a CPU interrupt request may be generated
depending on the mailbox interrupt mask register (MBIMR) and interrupt mask register (IMR)
settings.
• Remote frame reception
Two kinds of messages—data frames and remote frames—can be stored in mailboxes. A
remote frame differs from a data frame in that the remote transmission request bit (RTR) in the
message control register and the data field are 0 bytes long. The data length to be returned in a
data frame must be stored in the data length code (DLC) in the control field.
When a remote frame (RTR = recessive) is received, the corresponding bit is set in the remote
request wait register (RFPR). If the corresponding bit (MBIMR0 to MBIMR15) in the mailbox
interrupt mask register (MBIMR) and the remote frame request interrupt mask (IRR2) in the
interrupt mask register (IMR) are set to the interrupt enable value at this time, an interrupt can
be sent to the CPU.
Unread Message Overwrite: If the receive message identifier matches the mailbox identifier, the
receive message is stored in the mailbox regardless of whether the mailbox contains an unread
message or not. If a message overwrite occurs, the corresponding bit (UMSR0 to UMSR15) is set
in the unread message register (UMSR). In overwriting an unread message, when a new message
is received before the corresponding bit in the receive complete register (RXPR) has been cleared,
the unread message register (UMSR) is set. If the unread interrupt flag (IRR9) in the interrupt
mask register (IMR) is set to the interrupt enable value at this time, an interrupt can be sent to the
CPU. Figure 15.12 shows a flowchart for unread message overwriting.
Rev. 6.00 Mar 15, 2006 page 426 of 570
REJ09B0211-0600