The valid AFMR and AFIR register bit fields for sending TX messages to the controller are summarized in Table: CAN Message Acceptance Mask and Identifier Register Bit Fields. These fields are described in the Message Format section.
In the AFMR mask registers, enable (unmask) the compare functions for each field for the incoming RX message by writing a 1 to the bit field. In the AFIR registers, write the values that are to be compared to the incoming TX message.