SH7261 datasheet(898/1348 Pages) RENESAS

898 / 1348 page

Section 19 Controller Area Network (RCAN-ET) [R5S72611] [R5S72613]

Rev. 2.00 Sep. 07, 2007 Page 866 of 1312

REJ09B0320-0200

When RCAN-ET recognises the end of the Arbitration field while receiving a message, it starts

comparing the received identifier to the identifiers set in the Mailboxes, starting from Mailbox-15

down to Mailbox-0. It first checks the MBC if it is configured as a receive box, and reads LAFM,

and reads the CAN-ID of Mailbox-15 (if configured as receive) to finally compare them to the

received ID. If it does not match, the same check takes place at Mailbox-14 (if configured as

receive). Once RCAN-ET finds a matching identifier, it stores the number of Mailbox-[n] into an

internal buffer, stops the search, and goes back to idle state, waiting for the EndOfFrame (EOF) to

come. When the 6

th bit of EOF is notified by the CAN Interface logic, the received message is

written or abandoned, depending on the NMC bit. No modification of configuration during

communication is allowed. Entering Halt Mode is one of ways to modify configuration. If it is

written into the corresponding Mailbox, including the CAN-ID, i.e., there is a possibility that the

CAN-ID is overwritten by a different CAN-ID of the received message due to the LAFM used.

This also implies that, if the identifier of a received message matches to ID + LAFM of 2 or more

Mailboxes, the higher numbered Mailbox will always store the relevant messages and the lower

numbered Mailbox will never receive messages. Therefore, the settings of the identifiers and

LAFMs need to be carefully selected.

With regards to the reception of data and remote frames described in the above flow diagram the

clearing of the UMSR flag after the reading of IRR is to detect situations where a message is

overwritten by a new incoming message stored in the same mailbox while the interrupt service

routine is running. If during the final check of UMSR a overwrite condition is detected the

message needs to be discarded and read again.

Please note that in the case a received remote frame is overwritten by a data frame, both the

remote frame request interrupt (IRR2) and data frame received interrupt (IRR1) and also the

Receive Flags (RXPR and RFPR) are set. In an analogous way, the overwriting of a data frame by

a remote frame, leads to setting both IRR2 and IRR1.

In the Overrun Mode (NMC = '0'), only the first Mailbox will cause the flags to be asserted. So, if

a Data Frame is initially received, then RXPR and IRR1 are both asserted. If a Remote Frame is

then received before the Data Frame has been read, then RFPR and IRR2 are NOT set. In this case

UMSR of the corresponding Mailbox will still be set.

SH7261 Datasheet(PDF) 898 Page - Renesas Technology Corp