ST72561AR7-Auto datasheet(222/324 Pages) STMICROELECTRONICS

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beCAN controller (beCAN)

ST72561-Auto

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Doc ID 12370 Rev 8

By transmit request order:

the transmit mailboxes can be configured as a transmit FIFO by setting the TXFP bit in the

CMCR register. In this mode the priority order is given by the transmit request order.

This mode is very useful for segmented transmission.

Abort

A transmission request can be aborted by the user setting the ABRQ bit in the MCSR

request while the mailbox is in transmit state can have two results. If the mailbox is

transmitted successfully the mailbox becomes empty with the TXOK bit set in the MCSR

and CTSR registers. If the transmission fails, the mailbox becomes scheduled, the

transmission is aborted and becomes empty with TXOK cleared. In all cases the mailbox will

become empty again at least at the end of the current transmission.

Non-automatic retransmission mode

To configure the hardware in this mode the NART bit in the CMCR register must be set.

In this mode, each transmission is started only once. If the first attempt fails, due to an

arbitration loss or an error, the hardware will not automatically restart the message

transmission. At the end of the first transmission attempt, the hardware considers the

request as completed and sets the RQCP bit in the MCSR register. The result of the

transmission is indicated in the MCSR register by the TXOK, ALST and TERR bits.

Figure 100. Transmit mailbox states

17.4.2

Reception handling

For the reception of CAN messages, three mailboxes organized as a FIFO are provided. In

order to save CPU load, simplify the software and guarantee data consistency, the FIFO is

EMPTY

TXRQ=1

RQCP=X

TXOK=X

PENDING

RQCP=0

TXOK=0

SCHEDULED

RQCP=0

TXOK=0

Mailbox has

TRANSMIT

RQCP=0

TXOK=0

CAN Bus = IDLE

Transmit failed * NART

Transmit succeeded

Mailbox does not

EMPTY

RQCP=1

TXOK=0

highest priority

have highest priority

EMPTY

RQCP=1

TXOK=1

ABRQ=1

Transmit failed * NART

TME = 1

TME = 0

TME = 1

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