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OVERVIEW OF ENHANCED CAN CONTROLLERS FOR ST7 AND ST9 MCUS

ated handling for high priority messages and non-critical messages. This feature helps to re-

duce the real-time constraint on the application.

Filter Match Index

Once a message has been stored in the FIFO, the application will transfer the data to the

RAM. BxCAN provides a Filter Match Index, FMI, corresponding to the index of the filter the

message passed through. The FMI is stored in the FIFO with the received message. Because

of their wide spread distribution, CAN identifiers cannot be immediately used as an index to

the destination location of the data. The FMI provides a means of accessing a receive mes-

sage table directly.

Valid Message

A message is considered as valid when it has been received without error until the last but one

bit of the EOF field. And it passes through the identifier filtering successfully.

FIFO Overrun

The CAN core has its own message buffer and starts transferring the message to the FIFO

once the message is considered as valid. Thus an overrun condition will occur if four valid

messages have been received in the same FIFO but not handled by the application. Further-

more this mailbox in the CAN core guarantees that no erroneous message will overwrite a cor-

rect one already stored in the FIFO.

3.6 beCAN MAIN FEATURES

The basic enhanced CAN - called beCAN - supports:

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CAN protocol version 2.0 A, B Active

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Bit rates up to 1Mbit/s at 8MHz

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Two transmit mailboxes

– Priority by identifier or FIFO

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One receive FIFO with three stages

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Four scalable filters

– Identifier list feature

– Filter match index