AN1077 View Datasheet(PDF) - STMicroelectronics
Part Name
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MFG CO.
'AN1077' PDF : 14 Pages View PDF
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:
s CAN protocol version 2.0 A, B Active
s Bit rates up to 1Mbit/s at 8MHz
s Two transmit mailboxes
– Priority by identifier or FIFO
s One receive FIFO with three stages
s Four scalable filters
– Identifier list feature
– Filter match index
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