ST72561AR7-Auto datasheet(227/324 Pages) STMICROELECTRONICS

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ST72561-Auto

beCAN controller (beCAN)

Doc ID 12370 Rev 8

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Figure 103. Filtering mechanism - example

The example above shows the filtering principle of the beCAN. On reception of a message,

the identifier is compared first with the filters configured in identifier list mode. If there is a

match, the message is stored in the FIFO and the index of the matching filter is stored in the

filter match index. As shown in the example, the identifier matches with identifier #2 thus the

message content and MFMI 2 is stored in the FIFO.

If there is no match, the incoming identifier is then compared with the filters configured in

mask mode.

If the identifier does not match any of the identifiers configured in the filters, the message is

discarded by hardware without software intervention.

17.4.4

Message storage

The interface between the software and the hardware for the CAN messages is

implemented by means of mailboxes. A mailbox contains all information related to a

message; identifier, data, control and status information.

Transmit mailbox

The software sets up the message to be transmitted in an empty transmit mailbox. The

status of the transmission is indicated by hardware in the MCSR register.

Message Discarded

Identifier

n+1

Mask

Identifier

n+m

Mask

Identifier

Message Received

Ctrl

Data

Identifier #2 Match

Message

Stored

Receive FIFO

No Match

Found

n: number of single identifiers to receive

m: number of identifier groups to receive

n and m values depend on the configuration of the filters

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