Figure 13.12 Unread Message Overwrite Flowchart - Renesas H8SX/1520 Series Hardware Manual

(4)
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) in the unread message register
(UMSR) is set. In overwriting an unread message, the unread message register (UMSR) is set
when a new message is received before the corresponding bit in the receive complete register
(RXPR) has been cleared. If the unread interrupt flag (IRR9) in the interrupt mask register (IMR)
is set to enable interrupts at this time, an interrupt can be sent to the CPU. Figure 13.12 shows a
flowchart for unread message overwriting.
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Unread message overwrite
UMSR = 1
IRR9 = 1
IMR9 = 1?
No
Interrupt to CPU
Clear IRR9
Message control/message data read
End

Figure 13.12 Unread Message Overwrite Flowchart

Section 13 Controller Area Network (HCAN)
: Settings by user
: Processing by hardware
Yes
Rev. 3.00 Mar. 14, 2006 Page 497 of 804
REJ09B0104-0300