MikroElektronika PIC Microcontrollers PIC18 Manuel d'utilisateur télécharger pdf (Page 21)

The CAN module uses message acceptance filters and masks to determine if a

message in the MAB should be loaded into a receive buffer. Once a valid message is

received by the MAB, the identifier field of the message is compared to the filter

values. If there is a match, that message is loaded into the appropriate receive buffer.

The filter masks determine which bits in the identifier are examined with the filters.

The truth table in Table 9.3 shows how each bit in the identifier is compared against

Message Assembly Buffer

Identifier

Data and

Identifier

Data and

Identifier

RXB0 RXB1

Acceptance Filter

RXF1

Acceptance Filter

RXF4

Acceptance Filter

RXF5

Acceptance Filter

RXF0

Acceptance Filter

RXF3

Acceptance Filter

RXM2

Acceptance Mask

RXM0

Acceptance Mask

RXM1

Figure 9.13: Receive buffer block diagram

Table 9.3: Filter/mask truth table

Mask bit n Filter bit n Message identifier bit n001 Accept or reject bit n

0 Accept

1 0 0 Accept

1 0 1 Reject

1 1 0 Reject

1 1 1 Accept

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MikroElektronika PIC Microcontrollers PIC18 Manuel d'utilisateur Page 21