ST72561AR7-Auto datasheet(226/324 Pages) STMICROELECTRONICS

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beCAN controller (beCAN)

ST72561-Auto

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Doc ID 12370 Rev 8

to Figure 102. The identifier list or identifier mask mode for the corresponding

Mask/Identifier registers is configured by means of the FMCLx and FMCHx bits in the CFMR

bit the mode for the two most significant bytes of filter bank x.

Example 1:

●

If filter bank 1 is configured as two 16-bit filters, then the FMCL1 bit defines the mode of

the CF1R2 and CF1R3 registers and the FMCH1 bit defines the mode of the CF1R6

and CF1R7 registers.

●

If filter bank 2 is configured as four 8-bit filters, then the FMCL2 bit defines the mode of

the CF2R1 and CF2R3 registers and the FMCH2 bit defines the mode of the CF2R5

and CF2R7 registers.

Note:

In 32-bit configuration, the FMCLx and FMCHx bits must have the same value to ensure that

the four Mask/Identifier registers are in the same mode.

To filter a group of identifiers, configure the mask/identifier registers in mask mode.

To select single identifiers, configure the mask/identifier registers in identifier list mode.

Filters not used by the application should be left deactivated.

Filter match index

Once a message has been received in the FIFO it is available to the application. Typically

application data are copied into RAM locations. To copy the data to the right location the

application has to identify the data by means of the identifier. To avoid this and to ease the

access to the RAM locations, the CAN controller provides a filter match index.

This index is stored in the mailbox together with the message according to the filter priority

rules. Thus each received message has its associated Filter Match Index.

The Filter Match Index can be used in two ways:

●

Compare the filter match Index with a list of expected values.

●

Use the filter match index as an index on an array to access the data destination

location.

For non-masked filters, the software no longer has to compare the identifier.

If the filter is masked the software reduces the comparison to the masked bits only.

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 filter in identifier list mode prevails on an filter in mask mode.

●

A filter with full identifier coverage prevails over filters covering part of the identifier, e.g.

16-bit filters prevail over 8-bit filters.

●

Filters configured in the same mode and with identical coverage are prioritized by filter

number and register number. The lower the number the higher the priority.

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