DESIGN OF A CUSTOM ASIC INCORPORATING CAN™ AND 1 ...

are compared to the values contained in these registers; see example below and also Figure 4.6.
Thus always groups of eight identifiers can be defined to be accepted for any node.
Example: MSB LSB
The Acceptance Code Register (ACR) contains: 0 1 1 1 0 0 1 0
The Acceptance Mask Register (AMR) contains: 0 0 1 1 1 0 0 0
Messages with the following 11 – bit identifiers are accepted 0 1 x x x 0 1 0 x x x
(x = don’t care) ID.10 ID.0
Figure 4.6 CAN Node Message Acceptance Filtering [48].
At the bit positions containing a “1” in the AMR, any value is allowed in the composition
of the identifier. The AMR defines the bit positions, which are relevant for the comparison (0 =
relevant, 1 = not relevant). The same is valid for the three least significant bits. Thus 64
different identifiers are accepted in this example. The other bit positions must be equal to the
values in the ACR. For accepting a message all relevant received bits have to match the
respective bits in the ACR. Although using acceptance filters and acceptance masks does not
provide a CAN node with a physical address, it does however provide a means to limit what
types of messages and how many will be received into an individual CAN node’s receive
buffers.
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