STM8S datasheet(393/467 Pages) STMICROELECTRONICS

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DocID14587 Rev 14

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RM0016

Controller area network (beCAN)

427

Filter priority rules

Depending on the filter combination it may occur that an identifier passes successfully

through several filters. In this case the filter match value stored in the receive mailbox is

chosen according to the following rules:

–

A 32-bit filter takes priority over 16-bit filter which takes itself priority over 8-bit

filter.

–

For filters of equal scale, priority is given to the identifier List mode over the

identifier Mask mode.

–

For filters of equal scale and mode, priority is given by the filter number (the lower

the number, the higher the priority).

Figure 152. Filter banks configured as in the example in Table 65

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 #4 thus

the message content and FMI 4 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 disturbing the software.

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