Acceptance Filter
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SPRUI07–March 2020
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Controller Area Network (CAN)
13.10 Acceptance Filter
The identifier of the incoming message is first compared to the message identifier of the mailbox (which is
stored in the mailbox). Then, the appropriate acceptance mask is used to mask out the bits of the identifier
that should not be compared.
In the SCC-compatible mode, the global acceptance mask (GAM) is used for the mailboxes 6 to 15. An
incoming message is stored in the highest numbered mailbox with a matching identifier. If there is no
matching identifier in mailboxes 15 to 6, the incoming message is compared to the identifier stored in
mailboxes 5 to 3 and then 2 to 0.
The mailboxes 5 to 3 use the local-acceptance mask LAM(3) of the SCC registers. The mailboxes 2 to 0
use the local-acceptance mask LAM(0) of the SCC registers. For specific uses, see Figure 13-44.
To modify the global acceptance mask register (CANGAM) and the two local-acceptance mask registers
of the SCC, the CAN module must be set in the initialization mode (see Section 13.7.1).
In eCAN mode, each of the 32 mailboxes has its own local-acceptance mask LAM(0) to LAM(31). There is
no global-acceptance mask in the eCAN mode.
The selection of the mask to be used for the comparison depends on which mode (SCC or eCAN) is used.
13.10.1 Local-Acceptance Masks (CANLAM)
The local-acceptance filtering allows the user to locally mask (don't care) any identifier bits of the incoming
message.
In the SCC, the local-acceptance-mask register LAM(0) is used for mailboxes 2 to 0. The local-
acceptance-mask register LAM(3) is used for mailboxes 5 to 3. For the mailboxes 6 to 15, the global-
acceptance-mask (CANGAM) register is used.
After a hardware or a software reset of the SCC module, CANGAM is reset to zero. After a reset of the
eCAN, the LAM registers are not modified.
In eCAN mode, each mailbox (0 to 31) has its own mask register, LAM(0) to LAM(31). An incoming
message is stored in the highest numbered mailbox with a matching identifier.
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